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Ecophysiological assessment of western hemlock and western red cedar greenhouse stocktypes Major, John E. 1990

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ECOPHYSIOLOGICAL ASSESSMENT OF WESTERN HEMLOCK AND WESTERN RED CEDAR GREENHOUSE STOCKTYPES BY JOHN E. MAJOR B.Sc.F. The U n i v e r s i t y of Toronto, 1984 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE (FORESTRY) i n THE FACULTY OF GRADUATE STUDIES (Department of Forest Science) We accept t h i s t h e s i s as conforming to the re q u i r e d standard The U n i v e r s i t y of B r i t i s h ' Columbia A p r i l , 1990 © John E. Major, 1990 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department The University of British Columbia Vancouver, Canada DE-6 (2/88) i i ABSTRACT Western hemlock (Tsuga heterophyl la (Raf.) Sarg.) and western red cedar (Thuja p l i c a t a Donn) seedlings from four dormancy induct ion treatment(s) (DIT) ( i . e . long-day dry, long-day wet, short-day dry , and short-day wet) were planted on a high ava i lab l e s o i l moisture f i e l d s i t e i n B r i t i s h Columbia and monitored for p h y s i o l o g i c a l response and morphological development over the f i r s t growing season. Stomatal conductance (gwv) and net photosynthesis (Pn) were recorded over an environmental matrix of photosynthet ica l ly -2 -1 ac t ive r a d i a t i o n (PAR) (0 - 2.2 mmol m s ) and vapour pressure d e f i c i t (VPD) (0 - 2.5 or 4.0 kPa) on both f i r s t year grown and f u l l y developed second year f o l i a g e . To compare stocktypes, p h y s i o l o g i c a l data were c o l l e c t e d and analyzed i n the fo l lowing ways: (1) r e p l i c a t e d data at s table environmental condit ions once a month, (2) p h y s i o l o g i c a l response to one increas ing environmental v a r i a b l e using boundary l i n e a n a l y s i s , and (3) p h y s i o l o g i c a l response surface to two simultaneously changing environmental v a r i a b l e s . For western hemlock f i r s t year needles, short-day DIT had a higher gwv response to both increas ing VPD and PAR. Both short-day and moisture stressed DIT improved Pn response to PAR, and the combination had the highest response. Short-day DIT seedlings i n i t i a l l y were smal ler , shorter , had a better seedl ing water balance r a t i o and lower i i i shoot to root r a t i o . Short-day second year needles showed a s l i g h t l y higher gwv response to both increas ing VPD and PAR as compared to long-day seedl ings; however, they showed no treatment d i f ferences for Pn versus PAR. A l l stocktypes had s i m i l a r f i n a l morphological parameter values . For western red cedar f i r s t year f o l i a g e , moisture stressed DIT seedlings had greater Pn response to increas ing PAR and VPD. A l s o , moisture stressed seedlings gwv response to increas ing VPD and PAR was higher when compared to i t s ' non moisture stressed daylength counterpart . The long-day wet seedlings i n i t i a l l y had a larger root and shoot system as compared to the other stocktypes. Second year fo l iage exhib i ted no treatment d i f ferences for gwv and Pn response to PAR ' and VPD. A l l stocktypes had s i m i l a r f i n a l morphological parameter values . Attempts to test stocktypes at stable environmental condit ions proved, at times, d i f f i c u l t . P o t e n t i a l l y large measurement v a r i a t i o n due to atmospheric environmental changes, and not stocktype e f f ec t , could r e s u l t . Boundary l i n e a n a l y s i s , when used c o r r e c t l y and with s u f f i c i e n t data, o f fers a good stocktype assessment method which enables the i s o l a t i o n of a p h y s i o l o g i c a l response to one environmental v a r i a b l e . Three dimensional surface response technique was required to provide a c lear conceptual representat ion of two primary environmental v a r i a b l e s ' inf luence on seedl ing p h y s i o l o g i c a l response. i v TABLE OF CONTENTS Page LIST OF TABLES v i LIST OF FIGURES v i i LIST OF SYMBOLS xi ACKNOWLEDGEMENTS x i i INTRODUCTION 1 LITERATURE REVIEW Stomatal Conductance 3 Light Intens i ty 3 Evaporative Demand 5 Temperature 6 Carbon Dioxide Concentration 7 Plant Water Status 8 Photosynthesis 10 Light Intens i ty 10 Evaporative Demand and Plant Water Status. . . 11 Stomatal Conductance 12 Temperature 15 Carbon Dioxide Concentration 16 Greenhouse C u l t u r a l Treatments 16 Daylength 17 Moisture Stress 18 Boundary Line Analys is 19 P h y s i o l o g i c a l Response Models 20 Species Background Western Hemlock 23 Western Red Cedar 24 RESEARCH HYPOTHESIS AND OBJECTIVES 25 MATERIAL AND METHODS Plant Mater ia l 27 F i e l d Site Conditions 30 Morphological Assessment 31 Measurement of Site Environmental Conditions . . . 33 Monthly Measurement of Repl icated P h y s i o l o g i c a l Data at Stable Environmental Conditions 33. P h y s i o l o g i c a l Response to One Environmental Var iab le 35 P h y s i o l o g i c a l Response to Two Environmental Var iables 37 RESULTS WESTERN HEMLOCK Environmental Conditions . 39 Preplant Morphology 39 Morphology After One Growing Season 42 V Monthly Measurement of Repl icated Phys io log i ca l Data at Stable Environmental Conditions 42 P h y s i o l o g i c a l Response of F i r s t Year Needles . . . 47 P h y s i o l o g i c a l Response of Second Year Needles . . . 60 WESTERN RED CEDAR Environmental Conditions 73 Preplant Morphology . 73 Morphology After One Growing Season 73 Monthly Measurement of Replicated Phys io log i ca l Data at Stable Environmental Conditions 77 Phys io log i ca l Response of F i r s t Year Fol iage . . . 80 P h y s i o l o g i c a l Response of Second Year Fol iage . . . 92 DISCUSSION Morphological Response of Western Hemlock 105 Morphological Response of Western Red Cedar . . . . 107 P h y s i o l o g i c a l Measurements at Stable Environmental Conditions 108 P h y s i o l o g i c a l Response: One Environmental Var iab le Basic Physiology 110 Stocktype Effect 115 P h y s i o l o g i c a l Response: Two Environmental Var iables 117 Advantages and Limitat ions of Phenomenological Models 121 Appl ica t ions of Phenomenological Models 124 SUMMARY AND CONCLUSIONS 129 LITERATURE CITATION 133 APPENDICES ' 153 VITAE 159 vi LIST OF TABLES Table Page 1. S o i l water p o t e n t i a l on mois ture -contro l l ed f i e l d s i t e 40 2. Predawn water p o t e n t i a l of western hemlock from d i f f e r e n t dormancy induct ion treatments and s o i l temperature from stable environment data c o l l e c t i o n days 41 3. Morphological development of western hemlock seedlings from d i f f e r e n t dormancy induct ion treatments before f i e l d p lant ing and af ter one growing season on a f i e l d s i t e 43 4. Re lat ive growth rate of western hemlock seedlings from d i f f e r e n t dormancy induct ion treatments for the f i r s t growing season on a mois ture -contro l l ed f i e l d s i t e 44 5. Predawn water p o t e n t i a l of western red cedar from d i f f e r e n t dormancy induct ion treatments and s o i l temperature from stable environment data c o l l e c t i o n days 74 6. Morphological development of western red cedar seedlings from d i f f e r e n t dormancy induct ion treatments before f i e l d p lant ing and af ter one growing season on a f i e l d s i t e 75 7. Re lat ive growth rate of western red cedar seedlings from d i f f e r e n t dormancy induct ion treatments for the f i r s t growing season on a mois ture-contro l l ed f i e l d s i t e 76 v i i LIST OF FIGURES Figure Page 1. Morning (Mn) and afternoon (Af) measurements taken each month across the growing season for A) photosynthet i ca l ly act ive rad ia t ion (PAR), B) vapour pressure d e f i c i t (VPD), C) net photosynthesis (Pn), D) stomatal conductance (gwv), and E) xylem water p o t e n t i a l ( <\> x) for western hemlock seedlings from dormancy induct ion treatments: 1) long-day dry (LDD), 2) long-day wet (LDW), 3) short-day dry (SDD), and 4) short-day wet (SDW). S i g n i f i c a n t d i f ferences determined by ANOVA and Waller-Duncan mean separation test (p=0.05) are shown by d i f f e r e n t l e t t e r s . Days with no l e t t e r i n g ind ica te no s t a t i s t i c a l l y s i g n i f i c a n t treatment d i f f erences . . . 45 2. Stomatal conductance boundary l i n e ana lys i s response to vapour pressure d e f i c i t (VPD) from f i r s t year needles for western hemlock seedlings in dormancy induct ion treatments: 1) long-day dry (LDD), 2) long-day wet (LDW), 3) short-day dry (SDD), and 4) short-day wet (SDW) 4g 3. Stomatal conductance boundary l i n e analys i s response to photosynthet ica l ly act ive rad ia t ion (PAR) from f i r s t year needles for western hemlock seedlings i n dormancy induct ion treatments: 1) long-day dry (LDD), 2) long-day wet (LDW), 3) short-day dry (SDD), and 4) short-day wet (SDW) 4g 4. Stomatal conductance response to photosynthet ica l ly act ive rad ia t ion (PAR) and vapour pressure d e f i c i t (VPD) from f i r s t year needles of western hemlock f o r : A) long-day dry (LDD), B) long-day wet (LDW), C) short-day dry (SDD), and D) short-day wet (SDW). 52 5. Net photosynthesis boundary l i n e ana lys i s response to photosynthet ica l ly act ive r a d i a t i o n (PAR) from f i r s t year needles for western hemlock seedlings in dormancy induct ion treatments: 1) long-day dry (LDD), 2) long-day wet (LDW), 3) short-day dry (SDD), and 4) short-day wet (SDW) 55 6. Net photosynthesis boundary l i n e ana lys i s response to vapour pressure d e f i c i t (VPD) from f i r s t year needles for western hemlock seedlings i n dormancy induct ion treatments: 1) long-day dry (LDD), 2) long-day wet (LDW), 3) short-day dry (SDD), and 4) short-day wet (SDW) 55 v i i i Figure Page 7. Net photosynthesis response to photosynthet i ca l ly act ive rad ia t ion (PAR) and vapour pressure d e f i c i t (VPD) from f i r s t year needles of western hemlock fo r : A) long-day dry (LDD), B) long-day wet (LDW), C) short-day dry (SDD), and D) short-day wet (SDW). 59 8. Stomatal conductance boundary l i n e ana lys i s response to vapour pressure d e f i c i t (VPD) from second year needles for western hemlock seedlings i n dormancy induct ion treatments: 1) long-day dry (LDD), 2) long-day wet (LDW), 3) short-day dry (SDD), and 4) short-day wet (SDW) 52 9. Stomatal conductance boundary l i n e ana lys i s response to photosynthet ica l ly act ive r a d i a t i o n (PAR) from second year needles for western hemlock seedlings in dormancy induct ion treatments: 1) long-day dry (LDD), 2) long-day wet (LDW), 3) short-day dry (SDD), and 4) short-day wet (SDW) 62 10. Stomatal conductance response to photosynthet i ca l ly act ive rad ia t ion (PAR) and vapour pressure d e f i c i t (VPD) from second year needles of western hemlock f o r : A) long-day dry (LDD), B) long-day wet (LDW), C) short-day dry (SDD), and D) short-day wet (SDW). 65 11. Net photosynthesis boundary l i n e ana lys i s response to photosynthet i ca l ly act ive rad ia t ion (PAR) from second year needles for western hemlock seedlings in dormancy induct ion treatments: 1) long-day dry (LDD), 2) long-day wet (LDW), 3) short-day dry (SDD), and 4) short-day wet (SDW) 68 12. Net photosynthesis boundary l i n e ana lys i s response to vapour pressure d e f i c i t (VPD) from second year needles for western hemlock seedlings i n dormancy induct ion treatments: 1) long-day dry (LDD), 2) long-day wet (LDW), 3) short-day dry (SDD), and 4) short-day wet (SDW) 68 13. Net photosynthesis response to photosynthet ica l ly ac t ive rad ia t ion (PAR) and vapour pressure d e f i c i t (VPD) from second year needles of western hemlock f o r : A) long-day dry (LDD), B) long-day wet (LDW), C) short-day dry (SDD), and D) short-day wet (SDW). 71 14. Morning (Mn) and afternoon (Af) measurements taken each month across the growing season for A) photosynthet i ca l ly act ive r a d i a t i o n (PAR), B) vapour pressure d e f i c i t (VPD), C) net photosynthesis (Pn), D) stomatal conductance (gwv), and E) xylem water p o t e n t i a l (<\>x) for western red cedar seedlings from ix Figure Page dormancy induct ion treatments: 1) long-day dry (LDD), 2) long-day wet (LDW), 3) short-day dry (SDD), and 4) short-day wet (SDW). S i g n i f i c a n t d i f ferences determined by ANOVA and Waller-Duncan mean separation test (p=0.05) are shown by d i f f eren t l e t t e r s . Days with no l e t t e r i n g indicate no s t a t i s t i c a l l y s i g n i f i c a n t treatment d i f f erences . . . 79 15. Stomatal conductance boundary l i n e ana lys i s response to vapour pressure d e f i c i t (VPD) from f i r s t year needles for western red cedar seedlings i n dormancy induct ion treatments: 1) long-day dry (LDD), 2) long-day wet (LDW), 3) short-day dry (SDD), and 4) short-day wet (SDW) 82 16. Stomatal conductance boundary l i n e ana lys i s response to photosynthet ica l ly act ive r a d i a t i o n (PAR) from f i r s t year needles for western red cedar seedlings i n dormancy induct ion treatments: 1) long-day dry (LDD), 2) long-day wet (LDW), 3) short-day dry (SDD), and 4) short-day wet (SDW) 82 17. Stomatal conductance response to photosynthet i ca l ly act ive rad ia t ion (PAR) and vapour pressure d e f i c i t (VPD) from f i r s t year needles of western red cedar f o r : A) long-day dry (LDD), B) long-day wet (LDW), C) short-day dry (SDD), and D) short-day wet (SDW). 85 18. Net photosynthesis boundary l i n e ana lys i s response to photosynthet i ca l ly act ive rad ia t ion (PAR) from f i r s t year needles for western red cedar seedlings i n dormancy induct ion treatments: 1) long-day dry (LDD), 2) long-day wet (LDW), 3) short-day dry (SDD), and 4) short-day wet (SDW) 88 19. Net photosynthesis boundary l i n e ana lys i s response to vapour pressure d e f i c i t (VPD) from f i r s t year needles for western red cedar seedlings i n dormancy induct ion treatments: 1) long-day dry (LDD), 2) long-day wet (LDW), 3) short-day dry (SDD), and 4) short-day wet (SDW) 88 20. Net photosynthesis response to photosynthet ica l ly act ive rad ia t ion (PAR) and vapour pressure d e f i c i t (VPD) from f i r s t year needles of western red cedar f o r : A) long-day dry (LDD), B) long-day wet (LDW), C) short-day dry (SDD), and D) short-day wet (SDW). 91 X Figure Page 21. Stomatal conductance boundary l i n e ana lys i s response to vapour pressure d e f i c i t (VPD) from second year needles for western red cedar seedlings i n dormancy induct ion treatments: 1) long-day dry (LDD), 2) long-day wet (LDW), 3) short-day dry (SDD), and 4) short-day wet (SDW) 94 22. Stomatal conductance boundary l i n e analys i s response to photosynthet ica l ly act ive rad ia t ion (PAR) from second year needles for western red cedar seedlings in dormancy induct ion treatments: 1) long-day dry (LDD), 2) long-day wet (LDW), 3) short-day dry (SDD), and 4) short-day wet (SDW) 94 23. Stomatal conductance response to photosynthet i ca l ly ac t ive rad ia t ion (PAR) and vapour pressure d e f i c i t (VPD) from second year needles of western red cedar for : A) long-day dry (LDD), B) long-day wet (LDW), C) short-day dry (SDD), and D) short-day wet (SDW). 97 24. Net photosynthesis boundary l i n e analys i s response to photosynthet i ca l ly act ive r a d i a t i o n (PAR) from second year needles for western red cedar seedlings i n dormancy induct ion treatments: 1) long-day dry (LDD), 2) long-day wet (LDW), 3) short-day dry (SDD), and 4) short-day wet (SDW) 1 0 0 25. Net photosynthesis boundary l i n e ana lys i s response to vapour pressure d e f i c i t (VPD) from second year needles for western red cedar seedlings i n dormancy induct ion treatments: 1) long-day dry (LDD), 2) long-day wet (LDW), 3) short-day dry (SDD), and 4) short-day wet (SDW) 1 0 0 26. Net photosynthesis response to photosynthet i ca l ly act ive rad ia t ion (PAR) and vapour pressure d e f i c i t (VPD) from second year needles of western red cedar for : A) long-day dry (LDD), B) long-day wet (LDW), C) short-day dry (SDD), and D) short-day wet (SDW). 1 0 3 LIST OF SYMBOLS Symbol Uni ts <§ rate of change <\>x xylem water po tent ia l MPa Ci i n t e r n a l carbon dioxide concentration ppm co2 carbon dioxide ppm DIT dormancy induct ion treatment E t ranspi rat ion , -2 -1 mol m s gwv stomatal conductance -1 cm s LDD Long-day dry LDW Long-day wet PAR photosynthet ica l ly act ive rad ia t ion i -2 -1 mmol m s Pn net photosynthesis , -2 -1 umol m s RGR r e l a t i v e growth rate SDD Short-day dry SDW Short-day wet VPD vapour pressure d e f i c i t kPa x i i ACKNOWLEDGEMENTS F i r s t of a l l , I am thankful for the generous support to this research from the Forest Biotechnology Centre, B r i t i s h Columbia Research Corporat ion. Funding came from FRDA d irec t de l ivery research contract no. F52-41-010 and a FRDA contr ibut ion from the B r i t i s h Columbia Min i s t ry of Forests and Forestry Canada to the Forest Biotechnology Centre. I would l i k e to extend my sincere appreciat ion to members of my supervisory committee, Dr. D.P. Lavender, James T. Arnot t , and Dr. S .C. Grossnickle for the ir c r i t i c i s m s and suggestions. I am thankful to Sharon Zar i feh for her help and comments. Specia l thanks to Steven Grossnickle for his construct ive review, support, and f r i endsh ip . He was the person who introduced me to ecophysiology in 1982 and has been a gracefu l guide ever s ince . I am deeply gra te fu l to J e n n i f e r , my wife, whose support, encouragement, and love seemed to me to be endless. This thesis i s hers as much as i t i s mine. Last but not l ea s t , I thank God for the opportunity to learn more about the world around, and for weaving these and many other people who have contributed into my l i f e . 1 INTRODUCTION Successful re fores ta t ion demands an understanding of both the morphological and p h y s i o l o g i c a l responses of a v a i l a b l e species and stocktypes to f i e l d s i t e environmental cond i t ions . C u l t u r a l treatments, such as moisture stress and modified daylength, can be introduced at a reasonable cost i n the greenhouse to produce stocktypes that may be better prepared for f i e l d p l a n t i n g . Reforestat ion s i t e studies have shown stocktype d i f ferences in morphological development over a number of growing seasons (Arnott 1975, Wood 1983) . P h y s i o l o g i c a l response may be the basis for these d i f f erences . Few studies have been published which show the p h y s i o l o g i c a l response of pre-condit ioned trees af ter f i e l d p lant ing (Hobbs 1984, S e i l o r and Johnson 1985, Vance and Running 1985) . The goal of th i s ecophys io log ica l research study was to character ize the response of western hemlock and western red cedar greenhouse c u l t u r a l stocktypes to changing atmospheric environmental condit ions before and af ter bud f lush development. The two main gas exchange parameters to be assessed on a f i e l d s i t e were; net photosynthesis (Pn) , because i t i s basic to primary product ion, and stomatal conductance (gwv) because i t regulates water l o s s . One method used to study the e f fect of c u l t u r a l treatments i s to measure these ind ica tors i n response to d i f f eren t environmental condi t ions . Since there are various factors 2 invo lved , i t would be prudent to examine the seedling response to primary environmental v a r i a b l e s . The l i t e r a t u r e review examines the fo l lowing areas: (1) and (2) response of gwv and Pn to major environmental v a r i a b l e s , (3) inf luence of greenhouse c u l t u r a l treatments, (4) use of boundary l i n e a n a l y s i s , (5) p h y s i o l o g i c a l response models, and (6) species background. 3 LITERATURE REVIEW Stomatal Conductance Stomata are the primary pathway for carbon dioxide ( C O 2 ) t ransfer from the atmosphere into the mesophyll of needles. Stomatal conductance i s a measure of microscopic pore opening which open and close i n response to the environment and allow gas exchange. They are contro l l ed by complex means and the exact mechanisms which operate the opening and c lo s ing are not f u l l y understood (Kramer 1983). It i s known that stomata respond to: l i g h t i n t e n s i t y , evaporative demand, temperature, i n t e r n a l CC^ ( C i ) , and plant water s tatus . These factors w i l l each be discussed b r i e f l y . L ight Intens i ty Stomatal conductance response to photosynthet ica l ly ac t ive r a d i a t i o n (PAR) general ly exh ib i t s a dramatic — 2 —1 increase at low l i g h t l eve l s (up to 0.1 mmol m s ), and then a s l i g h t increase with further PAR increases (which has a lso been described as a rectangular hyperbola shaped response) (Leverenz 1981, Beadle et a l . 1985b, Higgins et a l . 1987). Seasonal ly , th i s response may vary for con i f er s . During the summer, gwv for Pseudotsuga menzies i i (Mirb.) Franco was s i m i l a r to the above, but during the autumn and winter gwv showed i n s e n s i t i v i t y to changing PAR (Meinzer 1982b). 4 Current ly there are two theor ies , d i r e c t and i n d i r e c t response, descr ib ing the mechanism of gwv response to PAR (Sharkey and Ogawa 1987). In d i r e c t response, guard c e l l s i n i t i a t e stomatal movement v i a l i g h t absorbing pigments. In i n d i r e c t response, as l i g h t l eve l s increase and Pn begins, guard c e l l s respond to decreased Ci l e v e l s . A review of th i s hypothesis w i l l be discussed l a t e r on i n the C i sec t ion . Observations of l i g h t responses i n epidermal s t r i p s with stomata (Ogawa et a l . 1978) and in i s o l a t e d guard c e l l protoplas ts (Zeiger 1983) have brought for th evidence that stomatal response to l i g h t i s separate from the Ci l e v e l . In a d d i t i o n , photosynthesis system II i n h i b i t o r s have been introduced which s t a b i l i z e d C i , and have provided evidence that stomata are sens i t ive to l i g h t only (Sharkey and Raschke 1981). Sharkey and Ogawa (1987) concluded that experimental evidence thus far indicates that gwv response to l i g h t i s independent of changes i n Ci and that d i r e c t response to l i g h t can be very strong. The magnitude of gwv response to PAR i s dependent on the environment in which needles were developed. Sun needles (needles developed i n f u l l sunl ight) could have up to 100% higher gwv response to increas ing l i g h t i n t e n s i t y as compared to shade needles (needles developed i n a shaded environment), e . g . , Lar ix decidua M i l l . (Leverenz and Jarv i s 1979), and Picea s i t chens i s (Bong) C a r r . (Benecke et a l . 1981). It has also been observed that shade needles opened 5 at lower PAR, as compared to sun needles (Sharkey and Ogawa 1987) . E v a p o r a t i v e Demand It has been wel l documented that gwv of many tree species decreases as vapour pressure d e f i c i t (VPD) increases (Benecke et a l . 1981, Grossnickle and Blake 1986, Sandford and J a r v i s 1986). This factor has been c i t e d as the major determinant of gwv during most of the growing season (Beadle et a l . 1985a). Vapour pressure d e f i c i t i s the amount of atmospheric moisture d e f i c i t between needle and a i r . Vapour pressure d e f i c i t i s based on a i r temperature and r e l a t i v e humidity around the needle, needle temperature, and r e l a t i v e humidity i n the stomata antechamber. There are two major, often i n t e r a c t i n g , contro l loops proposed for descr ib ing gwv response to VPD (Schulze 1986a). F i r s t l y , the feedback response. Exposure of seedlings to increas ing VPD i n i t i a l l y causes t r a n s p i r a t i o n to increase which i n turn leads to decreases in xylem water po tent ia l ( 4<x). As <\>x continues to decrease, "I* x threshold i s eventual ly surpassed and stomatal c losure r e s u l t s . Feedback response i s mostly i n i t i a t e d by root zone water res i s tance . I n s u f f i c i e n t root water absorption to shoot t r a n s p i r a t i o n balance produces a t r a n s p i r a t i o n lag which i s c h i e f l y responsible for the midday stomatal depression (Tenhunen et a l . 1987). 6 Secondly, i n the feedforward concept, gwv responds to atmospheric drought by d i r e c t d r y i n g of guard and epidermal c e l l s , even though <|<x i s w e l l above the tu r g o r l o s s p o i n t . Stomatal responses to VPD changes have been shown to behave independent of changes i n <|>x (Schulze and Kuppers 1979, Leverenz 1981, Osonubi and Davies 1980a). T h i s was f i r s t demonstrated by u s i n g i s o l a t e d epidermal s t r i p s (Lange et a l . 1971), observed i n detached l e a v e s (Raschke 1970), and whole p l a n t s d i f f e r i n g i n e c o l o g i c a l demands (Schulze e t a l . 1972). C h a r a c t e r i s t i c a l l y , a feedforward response shows a g e n t l e gwv d e c l i n e to i n c r e a s i n g e v a p o r a t i v e demand. Temperature In a review on c o n i f e r water r e l a t i o n s , H i n c k l e y e t a l . (1978) found t h a t the e f f e c t of a i r temperature on gwv of c o n i f e r s i s weak between 0 - 40°C w i t h gwv i n c r e a s i n g s l i g h t l y as temperature i n c r e a s e s . Beadle e t a l . (1985a, and b) found gwv was i n f l u e n c e d when a i r temperature was below 10°C. H a l l (1982) s t a t e s t h a t "the v a r i a t i o n of gwv response to temperature may be due to measurements under u n s p e c i f i e d and v a r y i n g l e v e l s of humidity". However, i f VPD i s taken i n t o account temperature does not need to be c o n s i d e r e d because temperature i s i n c l u d e d i n i t s ' c a l c u l a t i o n (Kaufmann 1976, Running 1976). N e v e r t h e l e s s , i f an ov e r n i g h t f r o s t event precedes measurements, gwv v a l u e s are s i g n i f i c a n t l y reduced and hence temperature must be co n s i d e r e d ( D e l u c i a 1987, D e l u c i a and Smith 1987). 7 Conifer research shows that as s o i l temperatures decrease, gwv decreases (Lopushinsky and Kaufmann 1984, Grossnickle and Blake 1985, Delucia 1986). Stomatal conductance decrease with s o i l temperature i s thought to be due to a greater resistance to water flow through roots within the soi l -plant-atmosphere continuum and greater water v i s c o s i t y (Kaufmann 1976, Grossnickle 1988). Carbon Dioxide Concentration Stomata response to Ci i s var ied and subject to d ispute . It has been suggested that changes in gwv to PAR is purely an i n d i r e c t response, re su l t ing from changes in Ci concentration produced by l ight - induced changes in Pn (Miedner and Mansfield 1968, Hasio 1973). However, research has shown that varying external CC>2 (hence modifying Ci) had l i t t l e af fect on gwv, e . g . , Picea s i tchens i s (Beadle et a l . 1979), Pinus s y l v e s t r i s L . (Jarv i s 1980), and Pseudotsuga menziesi i (Meinzer 1982b). Further tests varying Ci conducted at d i f f erent water stress l eve l s (-0.5 to -2.5 MPa) showed that <\> x had an ef fect on gwv, but this was not mediated by Ci (Beadle et a l . 1979). In add i t ion , tests -2 -1 varying Ci at various l i g h t l eve ls (0 to 1.3 mmol m s ) showed no apparent influence on gwv response to PAR (Jarvis 1980). The connection between Ci and gwv has not been r igorous ly es tabl i shed, and in view of information presented in the l i g h t in tens i ty sec t ion , gwv response to PAR appears 8 to be a d i r e c t response. T h e r e f o r e , w i t h c e r t a i n c o n i f e r s , there i s no evidence f o r a C i mediated i n f l u e n c e on gwv. Plant Water Status I t has been w e l l documented t h a t gwv tends to decrease when p l a n t s are s u b j e c t e d to drought (Kaufmann 1979, Pezeshki and Chambers 1986, S c h u l t e and M a r s h a l l 1983). The exact r e l a t i o n s h i p between gwv and <|<x has been c h a r a c t e r i z e d i n two d i s t i n c t ways f o r many t r e e s p e c i e s . The f i r s t c o n s i s t s of two phases with a t h r e s h o l d p o t e n t i a l above which there i s l i t t l e change i n gwv, but below which gwv decreases r a p i d l y , e.g., P i c e a s i t c h e n s i s (Beadle et a l . 1979), Pinus banksiana Lamb. ( G r o s s n i c k l e and Blake 1986). The second has the appearance of a p r o g r e s s i v e negative feedback system i n which gwv decreases g e n t l y with d e c r e a s i n g <|>x, e.g., P i c e a mariana ( M i l l . ) B.S.P., and P. g l a u c a ( G r o s s n i c k l e and Blake 1986), and Pinus c o n t o r t a Dougl. (Dykstra 1974). In order to r e c o n c i l e the two c o n f l i c t i n g models of responses, H a l l (1982) suggests t h a t the t h r e s h o l d model r e f l e c t s s h o r t - t e r m stomata response (minutes/hours), and the p r o g r e s s i v e model r e f l e c t s a long-term response (days). I t has been documented t h a t gwv e x h i b i t e d t h r e s h o l d type models when the f o l i a g e of s e v e r a l s p e c i e s was r a p i d l y d i s t u r b e d by d e t a c h i n g them ( H a l l and Hoffman 1976). P r o g r e s s i v e models were re p o r t e d when measurements of predawn water p o t e n t i a l taken over the growing season were 9 plo t t ed against mean d a i l y gwv (Running et a l . 1975), and maximum morning gwv (Running 1980). However Grossnickle and Blake (1986) reported both a threshold and a progressive model for species tested over the growing season, and hence f ee l that these response types may also be inherent . The mechanics of the plant water status inf luence on gwv begins with s o i l water s tatus . In most research i t i s assumed that the s o i l water status contro l i s exerted through l e a f water s tatus . Evidence i s now accumulating on a g r i c u l t u r a l plants (Gollan et a l . 1985, Turner et a l . 1985, Schulze 1986b) showing that gwv corre la tes with s o i l water supply but not with l ea f water s tatus . The mechanism by which the root water status controls gwv i s not known but Schulze (1986b) has hypothesized that stomata may respond d i r e c t l y to a s igna l from the roots under condit ions of drought. The s ignal i s thought to be re la ted to root metabolic a c t i v i t y , which may be re la ted to cytok in in product ion , which tend to open stomata and counteract the e f fec ts of ABA i n leaves . The amount of t r a n s p i r i n g area as compared to absorbing area can inf luence stomatal behavior. Comparing gwv d i u r n a l response d i f ferences between western hemlock and Douglas-f i r , Running (1976) suggests that shoot to root r a t i o , and/or d i f f e r i n g root absorption c a p a b i l i t i e s , were the causes. A study by Pere ira and Kozlowski (1977) points to the counteract ing e f fects of extensive l ea f area on gwv. 10 Photosynthesis Since carbon a s s i m i l a t i o n i s basic to primary product ion , a model developed for Pn was constructed to compare stocktypes. It i s known that Pn responds to the fo l lowing fac tors : l i g h t i n t e n s i t y , evaporative demand and plant water s tatus , gwv, temperature, and C i . L ight Intens i ty A major environmental var iab l e regulat ing Pn i s PAR (Beadle et a l . 1985b). Photosynthetic rate usua l ly exhib i t s a hyperbol ic response to PAR which i s s i m i l a r to gwv response to PAR. C h a r a c t e r i s t i c a l l y , th i s i s seen as a rapid c u r v i l i n e a r increase up to a l i g h t saturat ion l e v e l (0.4 --2 -1 0.8 mmol m s ), and then l eve l s o f f or increases s l i g h t l y -2 -1 to f u l l sunl ight (2.2 mmol m s ) e . g . , Picea s i t chens i s (Watts et a l . 1978), Lar ix decidua (Benecke et a l . 1981), and Pinus s y l v e s t r i s (Beadle et a l . 1985a). However, for a fores t canopy, Pn versus PAR i s a near l i n e a r r e l a t i o n s h i p due to mutual shading and the i n a b i l i t y of fo l iage i n the lower canopy l eve l s to reach l i g h t saturat ion (Beadle et a l . 1985b). The i n i t i a l phase of Pn i s the trapping of l i g h t energy. Photosynthesis i s a two step process; a dark react ion and a l i g h t reac t ion . The l i g h t react ion involves e l ec tron removal from water, release of oxygen, and a reduction process to form pyr id ine nucleot ide (NADH or NADPH), and adensosine triphosphate (ATP). These stable high 1 1 energy compounds are used i n the dark r e a c t i o n to reduce CO^ v i a the C a l v i n c y c l e ( S a l i s b u r y and Ross 1985). Up to a l e v e l of l i g h t s a t u r a t i o n , Pn i s l i m i t e d d i r e c t l y by photochemical energy supply; t h e r e a f t e r , the dark r e a c t i o n c a p a b i l i t y to f i x CO^ becomes the l i m i t i n g f a c t o r . F o l i a g e developed i n shaded h a b i t a t s have a lower c a p a c i t y f o r Pn than f o l i a g e developed i n h a b i t a t s of high s o l a r r a d i a t i o n . (Leverenz and J a r v i s 1979, Benecke et a l . 1981) . These d i f f e r e n c e s i n c a p a c i t y are a s s o c i a t e d with d i f f e r e n c e s i n l e a f and stomata anatomy (Schulze and H a l l 1982) . Evaporative Demand and Plant Moisture Status Tree s p e c i e s g e n e r a l l y show a constant l i n e a r d e c l i n e i n Pn, or feedforward response, to i n c r e a s i n g VPD e.g., Pseudotsuga m e n z i e s i i ( G r i e u et a l . 1988, Meinzer 1982a), Pinus c o n t o r t a and P i c e a s i t c h e n s i s (Sandford and J a r v i s 1986) Podocarpus o l e i f o l i u s Buchh. and P. r o s p i g l i o s i i P i l g . (Meinzer et a l . 1984). The same l i n e a r response i s found f o r Pn to d e c r e a s i n g s o i l moisture ( G r o s s n i c k l e et a l . 1990a). In e a r l i e r r e p o r t s i t has been assumed t h a t Pn decrease to i n c r e a s i n g VPD was l a r g e l y gwv r e l a t e d (Hasio 1973, Mederski e t a l . 1975) However, evidence i s now g a t h e r i n g which i n d i c a t e s t h a t t h i s response i s non st o m a t a l . Many recent s t u d i e s have shown t h a t C i does not d e c l i n e w i t h gwv decrease due to VPD (B r i g g s et a l . 1986, Wong et a l . 1 9 8 5 ) . Sharkey (1984), i n v e s t i g a t i n g Pn d e c l i n e to i n c r e a s i n g VPD 12 showed that by measuring Ci d i r e c t l y , the decrease in Pn occurred at the mesophyll and was not due to the stomata. The author suggested that increased t r a n s p i r a t i o n with higher VPD induced water d e f i c i t s at the s i t e s of evaporation, and th i s i n h i b i t s Pn. This hypothesis explains i n part why s o i l and atmospheric drought have a s imi lar a f fec t on Pn. Under moderate environmental condi t ions , when stomatal and non stomatal l i m i t a t i o n s to Pn are compared, the stomatal l i m i t a t i o n i s often quite smal l . Teskey et a l . (1986) estimated that stomatal l i m i t a t i o n s accounted for 20-30% of the Pn decl ine i n Pinus taeda L . subject to various environmental condi t ions . Shoot to root ra t io s can inf luence the water r e l a t i o n balance of seedl ings , and hence inf luence the fo l iage development through the e f fects of h on l ea f expansion. Interwoven through th i s i s the proper balance of needle area a v a i l a b l e for Pn, and the opportunity to photosynthesize free from water s t re s s . Schulze (1986b), states that at the whole plant l e v e l , plants can regulate carbon p a r t i t i o n i n g to roots i n response to water r e l a t i o n s , but the underlying mechanisms are obscure. Stomatal Conductance U n t i l as la te as the ear ly 1970's, i t was thought that gwv l a r g e l y regulated Pn by decreasing Ci l e v e l s . This was p a r t i a l l y a re su l t of the close c o r r e l a t i o n found between 13 gwv and Pn (v. d, Dreissche 1971) and no d i r e c t methods of measuring C i . More recent ly , a number of studies have shown that a var iab l e amount of Pn can be observed for a given gwv reading (Leverenz 1981, Beadle et a l . 1985a), and that changing VPD has a d i r e c t a f fec t on the photosynthetic apparatus at the mesophyll (Sharkey 1984). Photosynthesis and gwv respond to PAR and VPD independently of each other except under extreme condit ions ( i . e . at low PAR, and at high VPD) (Kuppers and Schulze 1985, Beadle et a l . 1985a). The rate of Pn tends to be propor t iona l to gwv only at low gwv, because i t i s the strongest l i m i t a t i o n . It appears that too much emphasis i s placed on water use e f f i c i e n c y and what i t may i n d i c a t e . On a re fores ta t ion s i t e , i f one p a r t i c u l a r plant i s e f f i c i e n t with water use, other competing plants w i l l use that ava i lab le water to benef i t t h e i r own growth. A p lant that can to l era te s tress and maintain p h y s i o l o g i c a l a c t i v i t y as water d e f i c i t s increase , w i l l grow more than seedlings that avoid s tress by c l o s i n g t h e i r stomata. Furthermore, during a period of drought, only s tress to lerant seedlings w i l l be able to develop an extensive root system and thereby increase water uptake (Liv ingston and Black 1988). In a study done with 3 coniferous species , Grieu et a l . (1988) found drought re s i s tan t Pseudotsuga macrocarpa exhibi ted the least conservative water use e f f i c i e n c y i n response to s o i l and 14 atmospheric drought as compared to P. menz ie s i i , and Cedrus  a t l a n t i c a . Stomatal behavior has been recent ly described operating i n r e l a t i o n to an "optimal" theory (Farquhar et a l . 1980) which suggests stomata funct ion to minimize water loss for a given amount of carbon ga in . In other words, stomata behave i n order to maintain a constant Pn and t r a n s p i r a t i o n (E) to changes ( § ) i n gwv r a t i o (@Pn/@gwv / @E/@gwv) over a v a r i e t y of environmental condit ions wi th in the operat ional range of p l a n t s . This was demonstrated by using d a i l y values in c o n t r o l l e d environments to humidity changes by Farquhar et a l . (1980) and to humidity and temperature changes by H a l l and Schulze (1980). However, Wil l iams (1983), working i n the f i e l d , and F i t e s and Teskey (1988), working in the laboratory and f i e l d , showed that stomatal behavior genera l ly d i d not conform to the above optimal behavior hypothesis . F i t e s and Teskey, studying Pinus teada, found that the gain r a t i o increased with VPD and suggested that stomata funct ion i n response to VPD, but that Pn may be inf luenced by non stomatal l i m i t a t i o n s and hence a l t e r the gain r a t i o . In another study, Meinzer et a l . (1984) working with t r o p i c a l species i n contro l l ed l a b o r a t o r i e s , found that Podocarpus o l e i f o l i u s exhibi ted a constant gain r a t i o , but Podocarpus r o s p i g l i o s i i d id not remain constant. 15 Temperature Leaf temperature response curve for Pn c h a r a c t e r i s t i c a l l y exhib i t s an inverted ' U ' with a broad plateau i n the middle region, e .g . between 15-25°C Pseudotsuga menzies i i (Meinzer 1982c ) , 10-25°C for Picea  engelmannii Parry ex Engelm. (Delucia and Smith 1987) and 10-25°C for Pinus s y l v e s t r i s (Kuppers and Schulze 1985) . It has been observed that optimum temperature and s ize of plateau for Pn i s dependent on c l i m a t i c precondi t ioning of the plant m a t e r i a l , and can s h i f t i n response to seasonal changes (Beadle et a l . 1985a, Delucia and Smith 1987) . Low Pn rates were h ighly corre la ted with low minimum s o i l temperature for Picea engelmannii (Delucia and Smith 1987) . Delucia (1986) working in a c o n t r o l l e d environment, found that root temperature had no e f fect on Pn between 10 to 20°C. However, gwv and Pn dec l ined dramat ica l ly below 8 °C . J u r i k et a l . (1988) , studying springtime recovery of Pinus strobus L . , observed the same response, and also found that Pn was more h ighly corre la ted with s o i l temperature at a depth of 30 cm than with a i r temperature, or s o i l temperature at more shallow depths. It has been suggested that although gwv decreases with Pn at low temperatures the dec l ine i n Pn i s due to non stomatal l i m i t a t i o n s because Ci was unchanged (Delucia 1986) . At the biochemical l e v e l , i t has been found that low needle temperatures reduce Pn because of reduced a c t i v i t y of the r ibulose biphosphate carboxylase-oxygenase (Rubisco) enzyme and the capacity for 16 e lec tron transport , and high temperatures reduce e lectron transport capacity and increase the rates of photoresp irat ion causing Pn to decl ine (Farquhar and Sharkey 1982) . Carbon Dioxide Concentration Carbon dioxide i s one of three basic inputs for photosynthesis , the others being water and l i g h t . The C 0 2 pathway from the atmosphere to u t i l i z a t i o n i n the ch lorop las t i s r e s t r i c t e d due to phys ica l and chemical l i m i t a t i o n s . According to laws governing d i f f u s i o n , i f there are l i m i t a t i o n s , larger gradients allow for faster rates of t r a n s f e r . Photosynthesis can almost always be increased by r a i s i n g the l e v e l of CO2 i n the atmosphere i f there are no other serious l i m i t a t i o n s to normal growth (Tinus 1974) . Adding CC>2 not only increases the rate of flow by d i f f u s i o n but a lso suppresses photorespirat ion in C^ plants at CO2 concentrations above 1000 p .p .m. (Tinus 1974, Sa l i sbury and Ross 1985) . This higher rate of Pn i s accomplished with no change i n water consumption, thus improving water use e f f i c i e n c y . Greenhouse C u l t u r a l Treatments Evidence i s accumulating which indicates the use of c e r t a i n seedl ing stocktypes are better sui ted to s p e c i f i c re fores ta t ion s i t e s (Arnott 1975, Hobbs 1984, Arnott and 17 Burdett 1988) . Current greenhouse container nurseries provide greater contro l of seedl ing physiology as compared to the outdoor bareroot nursery. Potent ia l for contro l of stocktype performance can be r e a l i z e d only by a thorough understanding of seedl ing response to environmental cues, and the procedures for provid ing them (Tinus 1981). In order to improve f i e l d p lant ing success and ear ly growth, c u l t u r a l treatments are appl ied to seedlings to induce dormancy and/or harden seedl ings . Two economically v i a b l e methods, daylength and moisture s t re s s , are being used i n c r e a s i n g l y by nurser ies to meet morphological gu ide l ine s . However, there i s l i t t l e information on how nursery c u l t u r a l prac t i ces a f fec t seedl ing physiology and subsequent development (Duryea 1985). Daylength Growth and development for many tree species i s regulated by photoperiod. Extended photoperiods have been shown to promote increased height and diameter growth and dry weight while reduced photoperiod have been shown to decrease these parameters (Arnott and M i t c h e l l 1981). Short-day causes rapid cessat ion of shoot growth and stimulated bud development, whereas free growth continues under long-day ( O ' R e i l l y et a l . 1989b). Research into examining seedl ing q u a l i t y of western hemlock stocktypes, treated with various daylength and moisture stress DIT, found short-day seedlings superior (Grossnickle et a l . 1990a) . Short-day 18 seedlings had the greatest co ld to lerance , highest root growth capacity at 5 ° C , highest osmotic p o t e n t i a l , and highest Pn at high s o i l moisture s tress condi t ions . In f i e l d p lantat ions i n the i n t e r i o r of B . C . and A l b e r t a , short-day treatment of Picea glauca (Moench) Voss and Pinus contorta showed higher s u r v i v a l and more rapid growth i n i t i a t i o n in the spring ( S i l i m et a l . 1989). Moisture Stress One of the f i r s t inves t igat ions into the e f fects of moisture s t re s s , as a precondi t ioning c u l t u r a l treatment, on Pn and gwv response was on Pinus taeda seedlings (Se i l er and Johnson 1985). The study revealed that moisture stressed seedlings were able to maintain Pn to much lower needle water po ten t ia l s than contro l treated seedl ings . This response was thought to be p a r t i a l l y a t t r i b u t e d to the s i g n i f i c a n t 0.45 MPa decrease i n needle osmotic p o t e n t i a l . On a study using contro l and prestressed sunflower p lant s , Matthews and Boyer (1984) found that Pn response to increas ing PAR was the same at high l ea f water p o t e n t i a l , but at low (stressed) l ea f water p o t e n t i a l , Pn of moisture stressed plants was as much as 100% higher than contro l p l a n t s . In a d d i t i o n , they recorded higher gwv for moisture stressed plants as compared to contro l p l a n t s . It was concluded that the major contr ibutor to Pn acc l imat ion of moisture stressed plants was non stomatal acc l imat ion . Matthews and Boyer (1984) also brought for th evidence that 19 water s tress pre -condi t ion ing provided cytoplasmic protec t ion of c h l o r o p l a s t . Boundary Line Analys i s Attempts to corre la te gwv values to p a r t i c u l a r environmental var iab le s c o l l e c t e d in the f i e l d have met with l i m i t e d success because gwv i s simultaneously affected by a number of environmental var iab le s (Jarv i s 1976), and includes data which show d i u r n a l h y s t e r e s i s . Hysteres is genera l ly develops af ter midpoint of the day, showing reduced p h y s i o l o g i c a l values for the same environmental condit ions (Helms 1970, L iv ings ton and Black 1987). Webb (1972), a lso a t t r i b u t e s the r e s u l t i n g scatter diagram to errors of measurement, v a r i a b i l i t y of the b i o l o g i c a l m a t e r i a l , and the o v e r a l l v a r i a t i o n caused by other i n t e r a c t i n g f a c t o r s . I f much data ( i . e . Pn) has been c o l l e c t e d from a wide range of condit ions a scatter diagram w i l l r e s u l t . The l i n e of best performance w i l l be evident when l i m i t s of response are reached, but w i l l not occur i f there i s no cause-and-e f fec t r e l a t i o n s h i p . A boundary l i n e represents the highest values of a cause factor under condit ions of an experiment. Arguments for existence of a boundary l i n e are b i o l o g i c a l rather than mathematical, because of a l l the contr ibut ing v a r i a b l e s , and f a c t o r s . Recognit ion of th i s l i n e and c a l c u l a t i o n of i t s equation may vary . To best describe the data some 20 researchers used hand drawn l ine s connecting the highest values (Goldste in et a l . 1985, L iv ings ton and Black 1987). This method places a l i n e so i t encloses a l l points which may include e r r o r s , thereby al lowing for overest imation. Others developed regression equations using best data (Webb 1972, Chambers et a l . 1985, Grossnickle and Arnott 1990). This method derives a l i n e by a l o g i c a l process which allows some dev ia t ion above and below i t , minimizing the c o n t r i b u t i o n of e r r o r . However, there are no means of c a l c u l a t i n g a true estimate of rea l e r r o r . The i n a b i l i t y to do t h i s i s not a serious problem i f boundary l i n e i s regarded simply as an a n a l y t i c a l device requ ir ing i n t e l l i g e n t i n t e r p r e t a t i o n (Webb 1972). P h y s i o l o g i c a l Response Models Quant i tat ive d e s c r i p t i o n of a p h y s i o l o g i c a l funct ion to one or mult ip le environmental condit ions summarizes complex processes for understanding and comparison. Mathematical models of photosynthesis and plant water loss contro l are a major object ive i n t e s t ing hypothesis or comparing species , genotypes, and stocktypes. Models of b i o l o g i c a l systems are works of mathematics and a r t , and only p a r t i a l l y simulate r e a l i t y (Passioura 1973). Model l ing of physiology can be d iv ided into two main categor ies ; de termin i s t i c (mechanistic) ; and pred ic t i ve (phenomenological). Determinis t ic models include a v a r i e t y of studies that are designed to quantify the underlying 21 biochemical and b iophys ica l processes involved in p h y s i o l o g i c a l funct ions , whereas phenomenological models are involved with empir ica l studies of p h y s i o l o g i c a l behavior in r e l a t i o n to observed environmental condit ions (Kaufmann 1982b). Both contribute to understanding the process inves t iga ted . According to H a l l (1982) a mechanistic model of gwv response to the environment would require adequate descr ip t ions of the fo l lowing submodels: (1) mechanics of guard c e l l wal l deformation and phys ica l r e l a t i o n s with adjacent c e l l s ; (2) biochemistry and biophysics of osmotic p o t e n t i a l contro l wi th in guard c e l l s and r e l a t i o n s with other epidermal c e l l s ; and (3) c h a r a c t e r i s t i c s of water so lute , and hormonal transport within leaves and throughout p l a n t s . H a l l continues by saying that a mechanistic model of stomatal response to environment would be cumbersome and h igh ly u n r e l i a b l e . P r e d i c t i v e models integrate a ser ies of independent steady state environmental condi t ions . Stomatal conductance response model might include the fo l lowing independent v a r i a b l e s ; PAR, VPD, temperature, plant water s tatus , and C i . The simplest approach i s by using mul t ip le c o r r e l a t i o n s t a t i s t i c s which h i g h l i g h t re la t ionsh ips and measure the ir s trength . Hinckley et a l . (1975), t e s t ing both a mult iple and s ing le var iab l e equation found that the mult iple equation provided poor estimates for l ea f surface res i s tance . It was stated that caution should be used when 22 empir ica l mul t ivar ia te models are used to determine the contr ibut ion of a s ingle var iab le from natura l environments. Research with p r e d i c t i v e models can be strengthened considerably by developing phenomenological models using c o n t r o l l e d environments, or by being based on boundary l i n e ana lys i s using l eas t squares regression analys i s to obtain input parameters (Hal l 1982). The main d r i v i n g environmental var iab le s for the p h y s i o l o g i c a l process of i n t e r e s t must f i r s t be i d e n t i f i e d . To e luc idate the main d r i v i n g var iab les many studies on various tree species have been studied in c o n t r o l l e d environments (Meinzer 1982a, and b, Higgins et a l . 1987). Phys io log i ca l response i s recorded in r e l a t i o n to a range of th i s environmental var iab le and a regression equation i s derived using environmental var iab le transformations . Three-dimensional representations to 2 main d r i v i n g environmental var iab le s were f i r s t presented by j o i n i n g a number of main in tersec t ions wi th in the bounds of the environmental matrix . E a r l i e s t research presentations of these 3-D graphs are by Hinckley et a l . (1975) showing Quercus alba L . stomatal res istance to VPD and predawn water p o t e n t i a l , Pere ira and Kozlowski (1977) showing stomatal res is tance and shoot water p o t e n t i a l to PAR and temperature, and Osonubi and Davies (1980b) showing Pn and gwv to PAR and fo l iage temperature. Studies showing some of the f i r s t l eas t square regression ca lcu la ted 3-D models were Thompson and Hinckley (1977), e x h i b i t i n g l ea f surface res istance and 23 xylem pressure po tent ia l to predawn xylem pressure po tent ia l and VPD for Quercus a lba; Meinzer (1982c) water use e f f i c i e n c y to PAR and VPD for Pseudotsuga menziesi i ; and Grossnickle and Reid (1985) showing gwv to l i g h t i n t e n s i t y and VPD, and showing gwv to xylem water p o t e n t i a l and VPD. These regress ion based models have the d i s t i n c t advantage of prov id ing an equation for pred ic t ions wi th in bounds of the environmental range s tudied . Species Background Western Hemlock (Tsuga heterophyl la (Raf.) Sarg.) An important coasta l timber species , western hemlock grows along the P a c i f i c coast from Alaska and B r i t i s h Columbia ( B . C . ) to northwestern C a l i f o r n i a . It grows east to the western slope of the Continental D iv ide . Best stands are found i n the humid coastal regions of B . C . , Washington, Oregon, and Alaska where frequent fog and r a i n provide moisture during the growing season. Western hemlock occurs on a wide v a r i e t y of s o i l types from sandstone to igneous rock m a t e r i a l . Western hemlock i s u s u a l l y a secondary species growing i n assoc ia t ion with Picea s i t chens i s and Pseudotsuga menz ie s i i , but sometimes dominates and occas iona l ly grows i n pure stands (Fowells 1965). S i l v i c u l t u r a l a t t r i b u t e s which make western hemlock a des i rab le tree species are as fo l lows; i t i s rated very shade t o l e r a n t , releases wel l a f ter long periods of suppress ion, and has good regeneration p o t e n t i a l af ter using 24 a wide range of harvest methods. In B . C . , approximately 5 m i l l i o n container-grown western hemlock seedlings were planted i n 1988-1989 ( O ' R e i l l y et a l . 1989a). Western Red Cedar (Thuja p l i c a t a Donn ex D. Don) Western red cedar grows from the coasta l regions of southern A l a s k a , south through the coasta l ranges of B . C . through western Washington and Oregon to northern C a l i f o r n i a . It grows in land to the Rocky Mountains, confined to regions having abundant p r e c i p i t a t i o n and high humidity. It seldom occurs i n pure stands, and then only over small areas. I t i s often associated with Tsuga he terophy l la , Picea  s i t c h e n s i s , Pseudotsuga menz ies i i , and true f i r s . In i n t e r i o r areas, i t grows with Pinus monticola Doug, ex D. Don, Lar ix o c c i d e n t a l i s N u t t . , Pinus contorta , Picea  engelmannii and Abies la s iocarpa (Hook.) Nutt . (Fowells 1965). The volume of mature western red cedar i n B . C . i s estimated at 824 m i l l i o n cubic meters. This represents 3.5% and 8.5% of the t o t a l mature timber volume of Canada and B . C . , r e spec t ive ly (Quenet and Magdanz 1988). S i l v i c u l t u r a l a t t r i b u t e s which make western red cedar a des irable tree species are; low s u s c e p t i b i l i t y to root rot and insect pests , shade to lerance , and tolerance to p lant ing i n mild f ros t pockets. In 1987, approximately 6.4 m i l l i o n seedlings were planted i n the Vancouver Forest Region (Curran and Dunsworth 1988) . 25 RESEARCH HYPOTHESIS AND OBJECTIVES Af ter reviewing the l i t e r a t u r e , i t was decided to l i m i t the number of environmental factors var ied to two. It has been shown that as s o i l water status decreases, p h y s i o l o g i c a l parameters response l i n e s show a s i m i l a r but progress ive decrease to changing VPD and PAR (Turner et a l . 1985) . Many researchers have found that when s o i l moisture i s not l i m i t i n g , PAR and VPD are the primary environmental factors that e f fec t gwv and Pn on a f i e l d s i t e (Kaufmann 1982b, Meinzer 1982c, Grossnickle and Reid 1985, Landsberg 1986) . Other important factors such as s o i l moisture, temperature, and Ci would be considered secondary factors and monitored c lo se ly or c o n t r o l l e d so that Pn and gwv data would not be adversely inf luenced. High s o i l moisture l e v e l would be maintained by watering r e g u l a r l y , p a r t i c u l a r l y the evening before measurements. Temperature would be recorded with each p h y s i o l o g i c a l measurement, and incorporated into the VPD v a r i a b l e . No data would be used i f a i r temperature was less than 0°C the evening p r i o r to measurements. Internal C O 2 would be ca lcu la ted for a l l p h y s i o l o g i c a l measurements and values above or 100 ppm below ambient would be d i scarded . It was hypothesized that western hemlock and western red cedar seedl ing stocktypes w i l l have d i f f e r e n t 26 p h y s i o l o g i c a l response patterns over a range of PAR and VPD on a s i t e where s o i l moisture i s contro l l ed on both: a) f i r s t year fo l iage (greenhouse grown f o l i a g e ) , and b) f u l l y expanded second year fo l iage ( f i e l d s i t e grown f o l i a g e . The fo l lowing i s a b r i e f l i s t i n g of research objec t ive s . They are expanded i n more d e t a i l i n the next s ec t ion . 1) Examine the change i n se lected morphological a t t r ibutes over one growing season. 2) Compile s t a t i s t i c a l comparison between stocktypes at stable environmental condit ions once a month for the growing season. 3) Examine the 2-D r e l a t i o n s h i p between Pn response to increas ing PAR and VPD. 4) Examine the 2-D r e l a t i o n s h i p between gwv response to increas ing VPD and PAR. 5) Character ize the 3-D response of Pn to simultaneously changing PAR and VPD l e v e l s . 6) Character ize the 3-D response of gwv to simultaneously changing PAR and VPD l e v e l s . 27 MATERIALS AND METHODS P l a n t M a t e r i a l Western hemlock (Tsuga h e t e r o p h y l l a (Raf.) Sarg.) seed ( B r i t i s h Columbia F o r e s t S e r v i c e (BCFS) R e g i s t e r e d Seedlot no. 3906; L a t . 48° 55' N, Long. 123° 55' W; e l e v a t i o n 340m) was s t r a t i f i e d at 1°C f o r 4 weeks before sowing. Western red cedar (Thuja p l i c a t a Donn) seed (BCFS R e g i s t e r e d S e e d l o t no. 7853; L a t . 4 8 ° 50' N, Long. 124° 00' W; e l e v a t i o n 525m) was soaked i n tap water f o r t h i r t y - s i x hours p r i o r to sowing. Both s p e c i e s were sown on March 2nd, 1987 i n BC/CFS 313A s t y r o b l o c k s (Beaver P l a s t i c s Ltd., Edmonton, A l t a . ) i n a 3:1 mixture of peat and v e r m i c u l i t e with dolomite lime added to ad j u s t the pH to 5.0 and coarse sand as seed cover. S e e d l i n g s were grown at the P a c i f i c F o r e s t r y Centre, V i c t o r i a , B.C. (Lat. 48° 28' N). The greenhouse environment was maintained a t a day/night temperature of 21/18°C, 50% r e l a t i v e humidity, and n a t u r a l l i g h t supplemented at ni g h t —2 -1 wi t h h i g h p r e s s u r e sodium vapor lamps ( i . e . 6 jc/mol m s ) to p r o v i d e a 16 hour p h o t o p e r i o d . S e e d l i n g s were watered and f e r t i l i z e d ( i . e . 20-20-20 NPK with m i c r o n u t r i e n t s ) twice weekly (500 mg 1~^), and biweekly with the heptahydrate form of f e r r o u s sulphate (155 mg l - ^ " ) . S e e d l i n g s were grown under the above greenhouse regime u n t i l J u l y 20, 1987 when mean s e e d l i n g shoot height had reached 15.8 and 16 .3 cm f o r western hemlock and western red cedar, r e s p e c t i v e l y . At t h i s p o i n t , one of four dormancy 28 induct ion treatments (DIT) were appl ied to one fourth of the seedl ing populat ion for each species . The dormancy treatments were as fo l lows: 1. Long-day wet (LDW): (contro l ) seedl ings continued to receive the above greenhouse regime u n t i l the end of August. 2. Long-day dry (LDD): seedlings had the extended photoperiod as in the above stated greenhouse regime, but on Ju ly 20, 1987 a moisture s tress treatment was i n i t i a t e d . 3. Short-day wet (SDW): seedlings continued to receive the above stated watering and f e r t i l i z a t i o n regime u n t i l the end of August (as i n 1) , but had photoperiod reduced to eight hours on August 1, 1987. 4. Short-day dry (SDD): seedl ings , on J u l y 20, 1987 had the moisture s tress treatment i n i t i a t e d and the photoperiod reduced to eight hours on August 1, 1987. A l l dormancy induct ion treatments were concluded on August 29, 1987, af ter which regular watering, f a l l f e r t i l i z a t i o n , temperature, and natural daylength regimes were implemented. F e r t i l i z e r (10-51-16 NPK with micronutr ients) was appl ied ( 500 mg l -''') weekly u n t i l November, and biweekly thereaf ter . Temperatures (day/night) were set at 2 0 / 1 0 ° C u n t i l September 15th, 1 7 / 8 ° C u n t i l October 10th, 1 5 / 5 ° C u n t i l October 15th, 13/4°C u n t i l November 11th, 1 0 / 3 ° C u n t i l November 18th, and 8 / 0 ° C u n t i l 29 seedlings were put into co ld storage ( 2 ° C ) on January 11th, 1988. In the moisture s tress treatment, s tyroblocks were allowed to dry down to approximately 2.63 kg below the i r saturated weight before rewaterng with f e r t i l i z e r so lut ion to sa tura t ion , and repeating the drying c y c l e . Average predawn and noon xylem pressure readings for each species at the end of drying cycles were -0.3 and -0.7 MPa for western hemlock and -0.4 and -1.0 MPa for western red cedar, r e s p e c t i v e l y . Seedlings were subjected to s ix drying cyc l e s . Many western hemlock shoots were wi l t ed by the afternoon of the l a s t day of each drying c y c l e . Thus western hemlock shoot w i l t was used as the ind i ca tor to end a drying cyc l e . Treatment s t a t i s t i c a l design was a modified L a t i n Square with DIT randomly assigned to four bench p o s i t i o n s . The two species were randomly assigned to opposite sides of each treatment block p o s i t i o n . Styroblocks wi th in a DIT were rotated every s ix weeks. No e f fect of bench l o c a t i o n was detected. From January 15 to February 20, 1988 seedlings were tested with an integrated stock q u a l i t y assessment procedure. These tests were organized into two areas c a l l e d mater ia l a t t r i b u t e s (d i rec t measurements), and performance a t t r i b u t e s (whole seedl ing response), as defined by Ri tch ie (1984). M a t e r i a l a t t r i b u t e tests included n u t r i t i o n , morphology (height, diameter, shoot and root dry weights, fo l iage and root surface areas, re la ted r a t i o s , and needle 3 0 primordia development), pressure-volume a n a l y s i s , soluble sugar a n a l y s i s , and seedl ing water movement. Performance a t t r i b u t e tests included root growth capaci ty ( s o i l pot, 5 and 22°C hydroponic t e s t ) , f ros t hardiness , low temperature response, and drought s tress response. Stock q u a l i t y assessment test resu l t s for western hemlock are described in Grossnickle et a l . (1990a), and for western red cedar in Grossnickle et a l . (1988). F i e l d S i te Condit ions The f i e l d s i t e was located at U n i v e r s i t y of B r i t i s h Columbia Forest Nursery, on the u n i v e r s i t y campus, Vancouver, B r i t i s h Columbia, Canada (Lat. 4 9 ° 15' N, Long. 1 2 3 ° 15' W). An area 20m x 20m was se lected which had been prev ious ly c u l t i v a t e d , but was l e f t fal low i n 1987. E leva t ion of the area i s 25m above sea l e v e l , with a gentle south fac ing s lope. The s i t e was r o t o - t i l l e d i n February 1988 p r i o r to f i e l d p l a n t i n g . Plow layer s o i l texture was a sandy-loam with 5.5 % organic matter, and i t was moderately wel l drained (appendix 1A). S o i l nutr ient ana lys i s taken i n March 1988 showed macronutrient d e f i c i e n c i e s in nitrogen and s u l f u r , and pH of 5.8 (appendix l a ) . A 20-20-20 granulated f e r t i l i z e r with micronutr ients was hand broadcasted and i r r i g a t e d into the s i t e i n March 1988. S o i l nutr ient ana lys i s i n July 1988 showed s a t i s f a c t o r y nitrogen l e v e l s , but low sul fur and potassium l eve l s (appendix IB) . 31 Seedlings were planted March 17-18, 1988 i n a randomized block design with repeated r e p l i c a t e s (appendix 2) . Two blocks were randomly assigned to each species . Seedlings from each DIT (4) were represented i n 5 randomly se lected rows for a t o t a l of 20 rows per block with 20 seedlings planted i n a 0.5m x 0.5m spacing per row. A t o t a l of 200 seedlings from each species/DIT were f i e l d planted. A four s p r i n k l e r head i r r i g a t i o n system was set up to contro l s o i l moisture d e f i c i t . The s i t e was watered r e g u l a r l y , p a r t i c u l a r l y on the days before recording of seedl ing p h y s i o l o g i c a l measurements. In add i t ion plant competit ion was contro l l ed by regu lar ly removing a l l vegetat ion from the s i t e mechanical ly . A s o i l moisture re tent ion curve was developed for the s i t e to allow s o i l moisture p o t e n t i a l ca l cu la t ions (appendix 3). Morphological Assessment Seedlings from each species/DIT (n=25) were measured p r i o r to f i e l d p l a n t i n g . Morphological parameters assessed include (1) shoot height , (2) root c o l l a r diameter, (3) fo l iage surface area, (4) root surface area, (5) shoot dry weight, ( 6 ) root dry weight, (7 & (8) shoot to root ra t io by dry weight and by surface area and, (9) seedl ing water balance r a t i o ( i . e . shoot dry weight/(root dry weight x root c o l l a r diameter)) . Dry weights were assessed af ter 48 hours at 65^ C. Needle and root area measurements were determined using a Li-3000 ( L i - C o r I n c . , L i n c o l n , Nebraska) area meter. 32 To assess growth af ter one growing season one randomly se lected seedl ing from each row was planted in buried c y l i n d r i c a l (30cm diameter, 30cm length) porous f e l t root bags (San Jac into C a p i t a l C o r p . , Houston, Texas). This f a c i l i t a t e d removal of 10 seedlings from each DIT 8 months af ter p lant ing to determine root and shoot development. Further d i scuss ion of the root analys i s technique can be found i n Grossnickle and Reid (1983). Except for root and fo l iage surface area, the same parameters as the preplant harvest were measured. The fo l lowing parameters were also measured (1) needle damage index, (2) root dry weight in container p lug , and (3) root dry weight outside container p lug . Needle damage was quant i f i ed by v i s u a l assessment of percent needles green where: 1=100%, 2=90-99%, 3=75-89%, 4=50-74%, 5=25-49%, 6=1-24%, and 7=0% green needles. The two species were analyzed separate ly . Data at the beginning of the growing season was analyzed using a one way ANOVA and Waller-Duncan mean separation t e s t . Due to b lock ing , end of the growing season data was analyzed as a two-way ANOVA. Experimental error was not s i g n i f i c a n t , and was combined with the sampling error to form a new mean square error term. The s i t e was plowed and appeared uniform but there was gentle slope hence the b l o c k i n g . The F-value ca l cu la ted showed that b locking was not s i g n i f i c a n t (p=0.05). 33 Measurement of S i te Environmental Condit ions When p h y s i o l o g i c a l measurements were c o l l e c t e d , s o i l samples were c o l l e c t e d at 1200h each day. S o i l moisture content was determined g r a v i m e t r i c a l l y , and water potent ia l s were determined from s o i l retent ion curves. I f the s o i l water p o t e n t i a l was found l i m i t i n g (below -0 .5 MPa), the p h y s i o l o g i c a l data for that day were d iscarded. Photosynthet ica l ly act ive r a d i a t i o n (PAR), and vapour pressure d e f i c i t (VPD) were taken simultaneously with net photosynthesis (Pn) and fo l iage conductance (gwv) readings using a L I - 6 2 0 0 CO2 porometer ( L i - C o r , I n c . ) . The PAR values were taken with a LI-1905-1 ( L i - C o r , Inc.) quantum sensor located on the porometer and was oriented perpendicular to incoming solar rad ia t ion at a l l t imes. Measurements of VPD were der ived by the porometer from chamber a i r temperature, chamber r e l a t i v e humidity, needle temperature and assumed 100% r e l a t i v e humidity i n the stomata antechamber. Monthly Measurement of Repl icated P h y s i o l o g i c a l Data at  Standard Environmental Condit ions Once each month during the growing season, A p r i l to September, a one day assessment of p h y s i o l o g i c a l data was c o l l e c t e d for each species . Data c o l l e c t i o n consisted of predawn xylem water p o t e n t i a l , then pressure chamber and porometer measurements taken from 0830h to lOOOh and 1300h to 1430h. This was done i n order to c o l l e c t 10 rep l i ca te s from each DIT during assumed periods of l eas t ( i . e . 0 8 3 0 -34 lOOOh) and greatest ( i . e . 1300-1430h) p h y s i o l o g i c a l s t ress . Days which were se lected had consistent l i g h t condit ions during c o l l e c t i o n periods ( i . e . c lear or constant cloud cover) . In a d d i t i o n , s o i l temperature (-10 cm) at 12h from two locat ions were recorded using a s o i l temperature probe. Shoot water p o t e n t i a l {<\> x) was measured on i n d i v i d u a l branch t i p s of seedlings using a pressure chamber ( S o i l Moisture Corp. Model 3005) according to R i t c h i e and Hinckley (1975). Shoot water p o t e n t i a l was measured on 10 seedlings se lected randomly from the ent ire populat ion . Net photosynthesis and gwv were measured with a Li-6200 ( L i - C o r Inc. ) portable porometer with a 1/4 1 (Li-6200-13) sample chamber. Conductance values refer to water vapour, and were ca lcu la ted from t r a n s p i r a t i o n rate and VPD (Schulze and H a l l 1982). For each sampling day, porometer data were co l l ec t ed from 10 preselected seedlings from each DIT. Needles were trimmed from the base of the twig to allow for closure of the gas exchange cuvette . In A p r i l and May, porometer samples were from f i r s t year f o l i a g e , while June through September, samples were from second year f o l i a g e . At the end of each data c o l l e c t i o n per iod , porometer samples were c l i p p e d . Tota l fo l iage surface area was determined using an Li-3100 area meter ( L i - C o r I n c . ) , m u l t i p l i e d by 2 for western hemlock, and 2.4 for western red cedar and then porometer measurements were reca lcu lated to represent t o t a l surface area . Both sides were included i n the ca l cu la t ions because both sides photosynthesize. The value of 2.4 was 35 determined, af ter repeated measurements, to best approximate t o t a l surface area ( inc luding width) of western red cedar. Morning and afternoon p h y s i o l o g i c a l data ( i . e . Pn, gwv and ^ x) were analyzed with analys i s of variance and s i g n i f i c a n t d i f ferences between DIT determined by Wal ler -Duncan mean separation test (Steele and T o r r i e 1980). Morning and afternoon environmental data were summarized for PAR and VPD. The changes over the season can be observed, but not compared s t a t i s t i c a l l y . P h y s i o l o g i c a l Response to One Environmental Var iab le Twenty to 30 randomly se lected seedlings from each DIT were prepared and marked from the f i e l d planted populat ion . The se lected seedlings were randomly measured for Pn and gwv over a range of PAR (0 to f u l l sunl ight) and VPD (low to the highest poss ib le on the s i t e ) . Data c o l l e c t i o n was environmentally d r i v e n , by t r y i n g to c o l l e c t data across the PAR x VPD matrix . Spec ia l a t tent ion was given to se l ec t ing hard to obtain PAR x VPD ( i . e . high PAR x low VPD and low PAR x high VPD). To help produce a range of environmental condi t ions , four 1.2m x 2.4m x 0.6m (w x 1 x h) shade racks were constructed. Two with 33% shade c lo th and two with 66% shade c l o t h were used. Racks were placed over a group of seedlings i n advance and measurements were not taken u n t i l one h a l f hour af ter placement. 36 Second year fo l iage response i s defined as p h y s i o l o g i c a l measurements on f u l l y developed second year fo l iage found on the same f i e l d s i t e . Treatment names remain the same to indicate greenhouse treatment h i s t o r y . Data was c o l l e c t e d and analyzed for f i r s t year fo l iage ( A p r i l and May) and for f u l l y developed second year fo l iage (July and August) . Most data were c o l l e c t e d over a 3-4 week time period with 125-150 data points obtained for each DIT. To avoid a hys teres i s e f f e c t , data measurement was r e s t r i c t e d from dawn to 1430h. Since data were c o l l e c t e d over a wide range of atmospheric environmental condi t ions , a boundary l i n e ana lys i s procedure was used to determine seedlings maximum Pn and gwv response to PAR and VPD condi t ions . This was then used to compare between d i f f e r e n t DIT. The boundary l i n e ana lys i s concept states that a scatter diagram's upper l i m i t of Pn or gwv measurements ( i . e . dependent var iab le ) i n response to an environmental var iab l e ( i . e . independent), known to l i m i t the dependent v a r i a b l e , ind icates the best p h y s i o l o g i c a l response to that p a r t i c u l a r environmental v a r i a b l e when other condit ions are not l i m i t i n g (Jarv i s 1976). This concept i s v a l i d as long as the two var iab les being examined have s u f f i c i e n t data to describe the ir r e l a t i o n s h i p . P h y s i o l o g i c a l ( i . e . Pn or gwv) data i n response to an environmental var iab l e was sys temat ica l ly taken from the upper region or layer of a scatter diagram, r e s u l t i n g in a 37 maximum p h y s i o l o g i c a l response data set for regression ana lys i s (Webb 1972). This procedure a lso reduced any p h y s i o l o g i c a l response overestimation to a s ingle environmental var iab le described by Chambers et a l . (1985). In the systematic c o l l e c t i o n procedure, the independent v a r i a b l e was p a r t i t i o n e d into segments with the greatest 3 to 4 p h y s i o l o g i c a l measurements from that segment included i n the maximum response data set (Grossnickle and Arnott 1990). The maximum response data set included 18 to 23 percent of the ent i re data set . Af ter some independent v a r i a b l e transformations, regression response models were then tested and compared by se l ec t ing one that had each parameter(s) s i g n i f i c a n t l y contr ibut ing to the model (p=0.05), and having the highest R-squared (Kleinbaum et a l . 1988). A t o t a l of 64 boundary l i n e response re la t ionsh ips were produced (2 species x 4 DIT x 2 fo l iage types x 4 r e l a t i o n s h i p s ) . P h y s i o l o g i c a l Response to Two Independent Environmental  Var iab l e s Response surfaces i n a 3-dimensional (3-D) coordinate system were generated using an empir ica l rather than mechanistic approach. The r e l a t i o n s h i p between (1) Pn to PAR and VPD, and (2) gwv to PAR and VPD were analyzed using mul t i var ia t e l i n e a r l eas t squares regress ion . The same data base used to generate the 2-dimensional (2-D) boundary l i n e response model were used for producing 3-D response surface 38 models. A l l data were used except for gwv data co l l ec t ed at r e l a t i v e humidit ies greater than 8 0 % . This r e s t r i c t i o n i s recommended by the manufacturer of the porometer (L i -Cor Inc. ) s ince ca l cu la t ions can be u n r e l i a b l e ( i . e . low gwv). To best describe the p h y s i o l o g i c a l response to two environmental v a r i a b l e s , a phenomenological model was developed. It was necessary to transform the independent v a r i a b l e s (PAR, VPD) into inverse , natura l logari thm, and quadrat ic values . Various models l a r g e l y based on the 2 -D responses generated were tes ted . Models were evaluated based on p a r t i a l F - te s t on each component of the model. Models with a l l components s i g n i f i c a n t l y contr ibut ing (p = 0 . 0 5 ) , and with the highest R-square, were considered the best . To compare DIT for a s p e c i f i c fo l iage type/species combination, the same model was used to generate each DIT. I f one component of one of the DIT models was not s i g n i f i c a n t ( p=0.05), i t was kept for comparison value . A t o t a l of 32 response surface models ( 2 species x 2 fo l iage types x 4 DIT x 2 r e la t ionsh ips ) were produced. 39 RESULTS WESTERN HEMLOCK Environmental Conditions S o i l water potent ia l s were only lower than -0.10 MPa three times and never lower than -0.37 MPa during the measurement season (Table 1) . Predawn xylem water potent ia l s were measured monthly and were never lower than -.64 MPa (Table 2) . In A p r i l and May measurement per iod , s o i l temperatures (-10 cm) were between 8 - 1 5 ° C , and were between 13 - 25°C for the rest of the measurement season. Morphology data showed no blocking e f f e c t , or b locking x treatment i n t e r a c t i o n at p=0.05 (unreported data) . Thus experimental and sampling errors were combined for a new data ana lys i s error term. Preplant Morphology Seedlings i n the LDW DIT had the larges t o v e r a l l shoot system with a greater height , diameter, and shoot dry weight (Table 3). Root dry weight and diameter were greater in non stressed DIT. Short-day DIT had a lower shoot to root r a t i o and a better seedl ing water balance r a t i o than long-day DIT. Long-day wet seedlings had s i g n i f i c a n t l y more needle surface area than LDD which had s i g n i f i c a n t l y more than short-day seedl ings . Non stressed seedlings had a greater root surface area as compared to water stressed seedl ings . 40 TABLE 1. Soil water potential on moisture-controlled f i e l d site. Date Sampled Soil Water Date Sampled Soil Water ( 1 9 8 8 ) Potential (- MPa) (1988) Potential (- MPa) April 21 0.05 July 6 0.07 30 0.06 18 0.09 May 5 0.08 19 0.36 6 0.04 21 0.04 19 0.05 25 0.08 20 0.08 26 0.09 23 0.06 28 0.04 24 0.06 29 0.08 25 0.06 Aug 3 0.08 30 0.07 22 0.11 June 3 0.08 23 0.18 29 0.09 Sept 22 29 0.05 0.06 4 1 TABLE 2 . Predawn water potential of western hemlock from different dormancy induction treatments and soi l temperature from stable environment data collection days. Dormancy Predawn Water Potential (- MPa) + 1 S.E. Induction Treatment April 30 June 3 July 6 July 19 Aug 23 Sept 22 . 1 2 + . 0 1 a 2 ) • 3 9 ± . 0 5 a .10+.02a . 5 7 ± . 0 9 a . 40+.09a . 2 6 ± . 0 3 a LDW .14+.02a .41+.08a . 1 0 ± . 0 2 a .62+.06a .47+.08ab .25+.Ola SDD . 13+ .Ola . 3 7 ± . 0 1 a .07+.02a .55+.04a .64+.05b .28+.03a SDW . 1 5 ± . 0 1 a .41+.02a . 1 0 ± . 0 1 a .64+.04a . 6 2 ± . 0 2 b . 2 6 ± . 0 4 a Noon S o i l Temp, at -10cm (°C) 8 15 19 25 19 13 LDD = Long-day dry LDW = Long-day wet SDD = Short-day dry SDW = Short-day wet A difference in the letter within each date indicates a significant difference between dormancy induction treatments at p •» 0.05 as determined by ANOVA and Waller-Duncan mean separation test. 42 Morphology Af ter One Growing Season A l l seedlings grew approximately 30 cm af ter 8 months in the f i e l d (Table 3 ) . Seedling shoot dry weights and diameters showed no s i g n i f i c a n t ( p=0.05) d i f f e r e n c e . SDW DIT had the lowest stem uni t s per cm and 1 . 0 needle damage index over the season. LDD DIT had the highest stem uni t s per cm and needle damage index of 1 . 7 8 with LDW and SDD showing intermediate values . New root development into the s o i l showed no s i g n i f i c a n t d i f ferences between DIT. Long-day DIT had greater ins ide the container plug root dry weight than short-day DIT and th i s d i f ference c a r r i e d over into t o t a l root dry weight sums. The three types of shoot/root ra t io s tested showed no s i g n i f i c a n t d i f ferences between DIT. Re lat ive growth rates for height , diameter, shoot and root dry weight are found in Table 4. Monthly Measurement of Repl icated P h y s i o l o g i c a l Data at  Stable Environmental Condi t ions . Afternoon p h y s i o l o g i c a l measurements were co l l ec ted under c lear sunny skies ( F i g . 1 A ) . Although photosynthet i ca l ly act ive rad ia t ion (PAR) l eve l s were s i m i l a r ( p a r t i c u l a r l y i n the afternoon) the vapour pressure d e f i c i t (VPD) l eve l s were var iab le with afternoon measurements ranging from 1 . 0 to 3 . 6 kPa ( F i g . IB) . Net photosynthesis (Pn) for f i r s t year fo l iage was lower than second year fo l iage under s i m i l a r environmental condit ions (May af . versus September a f . , F i g . 1 C ) . Pn Table 3. Morphological development of western hemlock seedlings from different dormancy induction treatments before f i e l d planting and after one growing season on a f i e l d s i t e . SHOOT ROOT SHOOT/ROOT RATIOS Dormancy Height Soot Dry Needle Needle Stem Container In S o i l Total Root Total Shoot Total Shoot Seedling Induction (cm) Collar Weight Surface Damage Units Plug Dry Dry Wt. Dry Wt. Surface Total Root New Root Water Treatment Diameter (g) Area Index' 1 1 (cm - 1) wt. (g) (9) (g) Area (by Wt.) (byWt.) Balance' 2 1 (cm) (cm2) (cm2) MARCH 15, 1988 -(Before Outplant) LDD< 3» 27 18+.61b ( 4 ) •27± 01b 1.27±.07bc 180.5t9.4b 1.00(5> - .35±.02c - .35±.02c 68.1t4.4c 3.85t 18b - 14 68t 86b LDW 31 52±.96a • 32± Ola 1.961.10a 272.9+14.5a 1.00 - .49±.04ab - .49±.04ab 90.7i6.5ab 4.221 16b - 13 65 ± 65b SDD 22 18t.57c • 28+ 01b 1.00±.03c 127.615.3c 1.00 - .40±.03bc - .40±.03bc 82.1t5.5bc 2.751 18a - 10 19+ 76a SDW 23 04±.52c .31+ Ola 1.281-08b 157.6+9.lb 1.00 - .53+.04a - .53±.04a 102.217.4a 2.601 12a - 8 69± 55a - NOVEMBER 15, 1988 -(8 Months After Outplant) LDD 57 28±2.42ab 1.01± 06a 22.14±2.75a - 1.78±.22 ( 5 ) 5.lit.46b 3.76±.31ab 4.80±.73a 8.55±.99ab - 2.59i 13a 4 73+ 27a 2 631 20a LDW 62 9411.85a 1.09± 02a 21.49±2.86a - 1.33±.17 4.33±.37ab 4.43±.34a 4.76±.61a 9.19±.84a - 2.541 38a 5 5511 10a 2 321 35a SDD 50 28±2.50b •93± 04a 15.73±1.99a - 1.67+.24 4.44±.73ab 2.89±.28b 3.52±.S8a 6.41±.79b - 2.481 15a 4 761 40a 2 681 16a SDW 53 47±2.51ab .94± 05a 18.17±2.32a 1.00±0 4.00±.24a 3.28±.28b 3.63±.51a 6.91±.72a 2.601 12a 5 231 44a 2 80i 16a CO (1) Needle damage index was catagorized as: 1=100%, 2=90-99*, 3=75-89*, 4=50-74*, 5=25-49*, and 6=1-24* green needles. (2) Seedling water balance r a t i o i s : shoot dry weight/(diameter x s o i l root dry weight). (3) LDD » Long-day dry LDW «• Long-day wet SDD » Short-day dry SDW = Short-day wet (4) Mean and standard error. A difference i n the l e t t e r for a morphological variable within each harvest date indicates a si g n i f i c a n t difference between dormancy induction treatment at p a 0.05 as determined by ANOVA and Waller-Duncan mean separation test. (5) No s t a t i s t i c a l analysis due to lack of variation i n one or more treatment(s). 44 TABLE 4 . Relative growth rate of western hemlock seedlings from different dormancy induction treatments for the f i r s t growing season on a moisture-controlled f i e l d site. Relative Growth Rates Dormancy Induction Treatment Height (cm/cm/mon.) Diameter (cm/cm/mon.) Shoot Dry Wt. (g/g/mon.) Total Root Dry Wt. (g/g/mon.) LDD1) .093 .165 .357 .399 LDW .086 .153 .299 .366 SDD .102 .150 .344 .347 SDW .105 .139 .332 .321 ^ LDD = Long-day dry LDW = Long-day wet SDD = Short-day dry SDW = Short-day wet. 45 Figure 1. Morning (Mn) and afternoon (Af) measurements taken each month across the growing season for: A) photosynthet ical ly act ive rad ia t ion (PAR), B ) vapour pressure d e f i c i t (VPD), C) net photosynthesis (Pn), D) stomatal conductance (gwv), and E) xylem water po tent ia l ( <p x) for western hemlock seedlings from dormancy induct ion treatments: 1) long-day dry (LDD), 2) long-day wet (LDW), 3) short-day dry (SDD), and 4) short-day wet (SDW). S ign i f i cant di f ferences determined by ANOVA and Waller-Duncan mean separation test (p=0.05) are shown by d i f f erent l e t t e r s . Days with no l e t t e r i n g indicate no s t a t i s t i c a l l y s i g n i f i c a n t treatment d i f f erences . Af Mn Af Mn Af Mn Af Mn Af Mn Af Apr May Jun Jul Aug Sep H LDD m L D f g SDD g | SDW 47 increased with time of year. No s i g n i f i c a n t d i f ferences were found between DIT for f i r s t year or second year f o l i a g e . Stomatal conductance (gwv) measurements for f i r s t year needles ( A p r i l and May) were higher i n short-day DIT seedlings than i n long-day seedl ings , but not s i g n i f i c a n t l y ( F i g . ID) . Maximum gwv value for f i r s t year needles obtained by SDW seedlings reached an average of 0.13 cm s~* i n A p r i l . Second year gwv measurements (June - September) showed no consistent treatment trends. Seedlings for a l l DIT exhibi ted higher gwv readings than f i r s t year fo l iage having a maximum value of 0.23 cm s~* i n September. Minimum xylem water p o t e n t i a l ( <l< x) was -1.0 MPa observed i n the afternoon readings of J u l y , August and September ( F i g . I E ) . Pressure-volume analys i s taken monthly showed that the turgor loss point was never higher than -1.5 MPa for LDW DIT (unpublished data) . P h y s i o l o g i c a l Response of F i r s t Year Needles Stomatal response of a l l seedlings indicated a s e n s i t i v i t y to changes i n VPD p a r t i c u l a r l y between 0.3- 1.0 kPa ( F i g . 2) . Beyond 1.0 kPa, stomatal response was constant with no further stomatal c losure seen up to a moderate VPD value of 2.5 kPa. Equations contained no constant since i t d id not s i g n i f i c a n t l y contribute to the model, whereas VPD and 1/VPD d i d at p=0.05. R-square values have been adjusted for the lack of constant and each indicate a reasonably good f i t 48 Figure 2. Stomatal conductance boundary l i n e ana lys i s response to vapour pressure d e f i c i t (VPD) from greenhouse needles for western hemlock seedlings in dormancy induct ion treatments: 1) long-day dry (LDD), 2) long-day wet (LDW), 3) short-day dry (SDD), and 4) short-day wet (SDW). Figure 3. Stomatal conductance boundary l i n e analys i s response to photosynthet ica l ly act ive rad ia t ion (PAR) from greenhouse needles for western hemlock seedlings i n dormancy induct ion treatments: 1) long-day dry (LDD), 2) long-day wet (LDW), 3) short-day dry (SDD), and 4) short-day wet (SDW). 49 0 .3 S T O M A T A L C O N D U C T A N C E ( c m s" L D D : Y = , 0 2 6 2 x + . 0 9 9 4 x " 1 : r 2 =.87 \\\\ L D W : Y = . 0 2 9 0 x + .0891x" 1 :r 2 =.84 \\\\ \\\\ S D D : Y = , 0 2 9 7 x + . 1 1 9 x " 1 : r 2 = , 8 5 \\\\ S D W : Y = . 0 3 5 3 x + .109x" 1 : r 2 =.74 W \ i i i i 0 .2 0.1 -0 .5 1 1.5 VPD (kPa) 2.5 0 .2 S T O M A T A L C O N D U C T A N C E ( c m s " 1 ) 0 . 1 5 -0.1 0 . 0 5 -L D D : Y = .114 + .011x :r 2=.14 • L D W : "Y "=". 121"+':01Ox"':r 2 '=.14'' S D D : Y = .152 + , 0 0 7 x ; r 2 = . 0 4 S D W : Y = .139 + , 013x : r 2 =.17 0 0 .5 PAR (mmol m 2 s"1) 1.5 i 2 LDD LDW SDD - - SDW 50 for a l l DIT. Regardless of moisture s tress treatment photoperiod was observed to have an e f fect on gwv to VPD response. Both short-day treatments had s i m i l a r and higher response to VPD than long-day treatments over the whole range of VPD recorded. Short-day gwv response was 0.02 cm s higher than long-day at the maximum VPD condit ion observed. Stomatal response show i n s e n s i t i v i t y to increas ing PAR -2 -1 from just above 0.1 up to 2.2 mmol m s ( f u l l sunl ight) ( F i g . 3) . There i s a s l i g h t increase i n gwv over th i s range re f l ec t ed i n the p o s i t i v e PAR c o e f f i c i e n t s , and greater than zero R-square values . A l i n e a r model best described the data , and both components s i g n i f i c a n t l y contributed to the equation. Since a constant was included i n the model, no adjustment to R-square was necessary. Although the R-square values were low t h i s does not r e f l e c t on how wel l the l i n e f i t s , but rather the lack of a strong c o r r e l a t i o n . Seedling DIT inf luenced gwv response to PAR. Both short-day DIT had 0.02-0.03 cm s - 1 higher than t h e i r long-day counterpart over the recorded PAR range. No moisture s tress e f fec t was observed. The model showing seedl ing gwv to simultaneous changes i n PAR and VPD i s shown i n f igure 4A-D for each DIT. At any given l e v e l of i r r a d i a n c e , gwv i s sens i t ive to VPD changes p a r t i c u l a r l y between 0.3-1.0 kPa. A l e v e l i n g o f f of gwv af ter 1.0 kPa was observed. A mostly l i n e a r response to PAR 5 1 Figure 4. Stomatal conductance (gwv) response to photosynthetically active radiation (PAR) and vapour pressure def ic i t (VPD) from f irs t year needles of western hemlock for: A) long-day dry (LDD), B) long-day wet (LDW), C) short-day dry (SDD), and D) short-day wet (SDW). The regression models are as follows: LgD: gwv = -0.0181 +0.0330(PAR) -0.000402(1/PAR) +0.0772(1/VPD): r = . 53 LDW: gwv = 0.0445 +0.0112(PAR) -0.000566(1/PAR) +0.0514(1/VPD): r = .48 SgD: gwv = -0.0242 +0.0384(PAR) -0.000422(1/PAR) +0.0937(1/VPD): r = . 51 SDW: gwv = 0.0568 +0.0192(PAR) -0.000667(1/PAR) +0.0446(1/VPD): r = .27 52 53 best described the gwv response at a l l VPD l e v e l s . From the 3-D response, data for the gwv to VPD 2-D response was most l i k e l y c o l l e c t e d when PAR was high. Moreover, most of the data for gwv to PAR 2-D response was most l i k e l y c o l l e c t e d at low VPD (approximately 0.5 kPa). Model l ing incorporated a constant, PAR, inverse PAR and inverse VPD as the best tested equation. A l l components s i g n i f i c a n t l y contributed to the model except inverse PAR. Inverse PAR was kept to c o r r e c t l y describe an observed b i o l o g i c a l response (pos i t ion gwv to zero at zero PAR), but at no inf luence to the rest of the response surface . R-square values obtained with th i s model are moderate in va lue . This r e f l e c t s an averaging of high R-square values achieved for gwv to VPD and low R-square values obtained for gwv to PAR. Short-day DIT had higher gwv response than long-day at high PAR. At high PAR and low VPD, SDD seedlings maintained a higher gwv than other DIT seedl ings . Although water stressed treatments d id not have an e f fec t on the gwv to VPD 2-D response, at low PAR moisture stressed seedlings stomata were almost closed at high VPD ( F i g . 4A ,C) . O v e r a l l SDW DIT seedlings maintained stomata open over the widest range of atmospheric environmental condi t ions . -2 -1 Between 0.05 and 0.6 mmol m s PAR, Pn exhibited a steep p o s i t i v e r e l a t i o n s h i p ( F i g . 5). For values greater -2 -1 than 0.6 mmol m s , PAR had a s l i g h t inf luence on Pn. -2 -1 Maximum Pn values ranged from 2.8 to 3.4 -imol m s for 54 Figure 5. Net photosynthesis boundary l i n e ana lys i s response to photosynthet i ca l ly act ive rad ia t ion (PAR) from f i r s t year needles for western hemlock seedlings in dormancy induct ion treatments: 1) long-day dry (LDD), 2) long-day wet (LDW), 3) short-day dry (SDD), and 4) short-day wet (SDW). Figure 6. Net photosynthesis boundary l i n e ana lys i s response to vapour pressure d e f i c i t (VPD) from f i r s t year needles for western hemlock seedlings in dormancy induct ion treatments: 1) long-day dry (LDD), 2) long-day wet (LDW), 3) short-day dry (SDD), and 4) short-day wet (SDW). 55 N E T P H O T O S Y N T H E S I S (fj. mo l m ' 2 s _ 1 ) 4 -, L D D : Y = 3.18 - 4 0 2 x +.0118x" 1 + .949lnx : r 2 = . 9 6 L D W : Y = 3 . 6 7 - . 8 9 7 x +.0105x" 1 + i . i 8 3 l n x : r 2 = . 9 5 S D D : Y = 4 . 7 2 - 1 . 2 6 9 x +.0265x" 1 +1.616lnx : r 2 = . 9 4 S D W : Y 5 9 7 x +.0125x~ 1+1.132lnx : r 2 = . 9 3 0 0 .5 PAR (mmol nrfV1) 1.5 N E T P H O T O S Y N T H E S I S ( M m o l r r f 2 s " 1 ) . L D D : . Y . =..3.00. - ...I96x.;r. 2. =.09.. L D W : Y = 3 . 0 7 - . 2 7 5 x : r 2 =.48 S D D : Y = 3 . 0 7 - .127x ;r 2 = .02 S D W : Y = 3.21 - , 3 6 5 x : r 2 =.28 "T" 2 0 0 .5 1 1.5 VPD (kPa) 2.5 LDD LDW SDD - SDW 56 LDW and SDD seedl ings , r e spec t ive ly . The l i g h t compensation _2 point for western hemlock seedlings i s 0.02 - 0.03 mmol m s~* (unreported data) . Equations which best described the data consisted of constant, PAR, inverse PAR, and natural logarithm of PAR. Each component s i g n i f i c a n t l y contributed to the response model. R-square values were very high for a l l treatments i n d i c a t i n g that PAR accounts for a large measure of v a r i a t i o n found in Pn. Seedling DIT inf luenced Pn response to PAR. Below 0.6 -2 -1 mmol m s , SDD DIT seedlings had greater Pn response compared to other DIT. At PAR l eve l s greater than 0.6 mmol -2 -1 m s , seedlings i n SDD had the greatest response followed by SDW, LDD and LDW, respec t ive ly . Moisture stressed seedlings had higher values than the i r non moisture stress counterparts . In a d d i t i o n , short-day seedlings had higher values compared to t h e i r long-day counterparts . This ind icates that moisture stressed / daylength treatment(s) inf luenced the Pn response for western hemlock seedl ings . Net photosynthesis decreased with increas ing VPD for a l l treatments ( F i g . 6) . A l i n e a r equation was found to best describe the data with both components s i g n i f i c a n t l y contr ibut ing to the model. R-square values for each DIT equation were r e l a t i v e l y low. Since a boundary l i n e analys is of data was used to describe the response, the low R-square values showed a weak r e l a t i o n s h i p , not a lack of f i t between Pn and VPD over the range of VPD values measured. 57 At low VPD l eve l s (0.5-1.0 kPa) a l l DIT seedlings showed s i m i l a r Pn response. As VPD increased, SDD DIT seedlings maintained Pn s imi lar to values found at low VPD. Net photosynthesis response to simultaneous changes in PAR and VPD for each DIT i s shown i n f igures 7 A - D . At any given l e v e l of VPD, Pn i s very responsive to PAR changes -2 -1 e s p e c i a l l y between 0 and 0.6 mmol m s . Above th i s l i g h t l e v e l , or approximate saturat ion po in t , Pn remained consistent or increased moderately depending on DIT. Note, i t was necessary to p o s i t i o n the best model equation through -2 -1 0 mmol m s , thus the l i g h t compensation point i s not shown. At any se lected value of PAR, Pn decreased l i n e a r l y with increas ing VPD. The best equation included the fo l lowing components; constant, PAR, inverse PAR, natural logarithm of PAR, and VPD. These components also best described the 2-D boundary l i n e ana lys i s ( F i g . 5 and 6) . A l l components s i g n i f i c a n t l y contr ibuted to the model. An i n t e r a c t i o n term was introduced but proved to be n o n - s i g n i f i c a n t . R-square values are r e l a t i v e l y high (0.7-0.85) showing that PAR and VPD strongly account for the Pn v a r i a t i o n . Comparing seedl ing treatments, Pn response to PAR at low VPD showed a s i m i l a r ranking and response as the 2-dimensional boundary l i n e analys i s ( F i g . 5) . SDD DIT seedlings had the highest response followed by SDW, LDD, and LDW, r e s p e c t i v e l y . Net photosynthesis dropped 30 to 35% as VPD increased to 2.5 kPa ( F i g . 7A-D). S imi lar ranking, but 58 Figure 7. Net photosynthesis (Pn) response to photosynthet ical ly ac t ive rad ia t ion (PAR) and vapour pressure d e f i c i t (VPD) from f i r s t year needles of western hemlock, for : A) long-day dry (LDD), B) long-day wet (LDW), C) short-day dry (SDD), and D) short-day wet (SDW). The regression models are as fol lows: LDD: Pn = 2.993 -0.263(PAR) +0.0131(1/PAR) +0.871(In(PAR) ) -0.422(VPD): r = .83 LDW: Pn = 3. 294 -0.525(PAR) +0.0078(1/PAR) +0.951(In(PAR) ) -0.344(VPD): r = .80 SDD: Pn = 3.416 -0.425(PAR) +0.0202(1/PAR) +1.066(In(PAR)) -0.446(VPD): r = .70 SDW: Pn = 3.115 -0.333(PAR) +0.0095(1/PAR) +0.893(In(PAR)) -0.388(VPD): r = .85 59 60 with not as pronounced Pn d i f f erences , occurred at the highest VPD l e v e l s . O v e r a l l , SDD seedlings were best able to maintain a higher l e v e l of Pn over the measured range of environmental condit ions compared to other DIT. P h y s i o l o g i c a l Response of Second Year Needles Stomatal conductance exhibi ted a c u r v i l i n e a r decrease with increas ing VPD with p a r t i c u l a r s e n s i t i v i t y between 1.0-2.0 kPa ( F i g . 8) . From VPD l eve l s of 2 .0-3 .8 , gwv continued to decrease, but not as r a p i d l y . At a VPD l e v e l of 2.0 kPa, gwv response for SDW DIT seedlings increased 33% and for LDW DIT seedlings gwv response increased 60% over f i r s t year needle. The best equation included VPD and 1/VPD and no constant was used since i t d id not s i g n i f i c a n t l y contribute to the model. The R-square values have been adjusted for lack of constant component and range from 0.60-0.66. No d i f ferences between DIT were observed for gwv at low VPD l e v e l s . As VPD increased, SDW DIT seedlings maintained a s l i g h t l y higher gwv than LDD, SDD and LDW, respec t ive ly . Compared to f i r s t year needles, treatment ranking was s i m i l a r except that LDD seedlings performance had improved, and o v e r a l l DIT di f ferences had decreased. A gwv increase of 30-50% was observed for a l l DIT seedlings as PAR increased ( F i g . 9) . At low PAR (0.1 mmol -2 -1 m s ) a moderate gwv increase of 25-30% was observed for a l l DIT seedlings compared to f i r s t year needles. At PAR 61 Figure 8. Stomatal conductance boundary l i n e analys i s response to vapour pressure d e f i c i t (VPD) from second year needles for western hemlock seedlings i n dormancy induct ion treatments: 1) long-day dry (LDD), 2) long-day wet (LDW), 3) short-day dry (SDD), and 4) short-day wet (SDW). Figure 9. Stomatal conductance boundary l i n e ana lys i s response to photosynthet i ca l ly act ive rad ia t ion (PAR) from second year needles for western hemlock seedlings i n dormancy induction treatments: 1) long-day dry (LDD), 2) long-day wet (LDW), 3) short-day dry (SDD), and 4) short-day wet (SDW). 62 S T O M A T A L C O N D U C T A N C E ( c m s " 1 ) 0 1 2 3 4 VPD (kPa) S T O M A T A L C O N D U C T A N C E ( c m s " 1 ) 0 . 3 i 0 -\ 1 1 1 r 0 0 . 5 ' 1 1.5 2 PAR (mmol m'V1) LDD — LDW SDD - - SDW 63 -2 -1 greater than 2.0 mmol m s , short-day seedlings response increased 40% while long-day seedlings increased by 75-85% compared to f i r s t year needles. A l i n e a r model best described the data with both components s i g n i f i c a n t l y contr ibut ing to the equation. R-square values were r e l a t i v e l y low, due to the hor izonta l r e l a t i o n s h i p between gwv and PAR. Seedling DIT inf luenced gwv response to PAR. Short-day DIT performed better than long-day DIT over the ent ire range of PAR; however, the d i f ference between short-day and long-day DIT seedl ing response was s l i g h t at high PAR. The f igures showing second year gwv response to simultaneous changes in PAR and VPD for a l l DIT are seen in f igures 10A-D. For any PAR, gwv i s responsive to VPD changes p a r t i c u l a r l y at values less than 1.5 kPa and greater than 3.5 kPa. From 0 to 1.5 kPa, gwv rap id ly decreased with increas ing VPD. Between 1.5 and 3.5 kPa, gwv decreased s l i g h t l y with increas ing VPD. For values greater than 3.5 kPa, gwv dec l ined to a point of stomatal c losure at -2 -1 approximately 4.0 kPa. From 0.1 mmol m s to f u l l sun l ight , a l i n e a r response best describes the gwv response to PAR at a l l l eve l s of VPD. Note the shape of gwv to VPD from the 3-D graph i s not the same as the 2-D gwv versus VPD graph. This i s because only the best values were used i n the boundary l i n e response and hence the method was not able to pick up the o v e r a l l decrease i n gwv at the highest VPD values measured. 64 Figure 10. Stomatal conductance (gwv) response to photosynthet ica l ly act ive rad ia t ion (PAR) and vapour pressure d e f i c i t (VPD) from second year needles of western hemlock for: A) long-day dry (LDD), B) long-day wet (LDW), C) short-day dry (SDD), and D) short-day wet (SDW). The regression models are as fol lows: LDD: gwv = 0.0315(PAR) -0 . 000171 ( 1/PARi +0()161(VPD) -0.107(ln(VPD)) -0.337(VPD) : r . .38 LDW: gwv = 0.0415(PAR) +0.001725(1/PAR1 +0,159(VPD) -0.102(ln(VPD)) -0.037(VPD) : r = .58 SDD: gwv = 0.0391(PAR) +0.001156(1/PARI +0,158(VPD) -0.106(ln(VPD)) -0.035(VPD) : r = .40 SDW: gwv = 0.0231(PAR) +0.000334(1/PAR) +0,189(VPD) -0.098(ln(VPD)) -0.041(VPD) : r = .39 65 66 Best equations included the fo l lowing components; PAR, inverse PAR, VPD, natural logarithm of VPD, and VPD squared. A l l components s i g n i f i c a n t l y contributed to the model except inverse PAR. Inverse PAR was kept to c o r r e c t l y describe an observed b i o l o g i c a l response (pos i t ion gwv to zero at zero PAR), but at no inf luence to the rest of the response surface . A constant d id not contribute to the model, hence the R-square values have been appropr ia te ly adjusted. R-square values were i n the 0.38-.58 range. Seedling DIT moderately affected second year needle gwv response to varying PAR and VPD. At low l i g h t l eve l s (0.1--2 -1 0.5 mmol m s ) and moderate to high VPD l eve l s (1.5-4.0 kPa) SDW DIT seedlings exhibi ted the greatest gwv response. During high VPD l eve l s (3.5-4.0 kPa), short-day and LDD DIT seedlings had higher gwv response than the LDW DIT _2 seedl ings . At moderately high PAR l eve l s (1.0-1.5 mmol m s - * ) , and low to moderate VPD l eve l s ( less than 3.5 kPa), a l l DIT seedlings had s i m i l a r response. Second year needles, s i m i l a r to f i r s t year needles, show Pn r i s e r a p i d l y to a l e v e l of l i g h t saturat ion (0.75 -2 -1 mmol m s ) ( F i g .11). As PAR increases , Pn values remained unchanged. The observed l i g h t compensation point d id not -2 -1 change s i g n i f i c a n t l y from 0.02-0.03 mmol m s as recorded for f i r s t year needles (unreported data) . The equation which best described the data consisted of a constant, PAR, inverse PAR, and natural logarithm of PAR. 67 Figure 11. Net photosynthesis boundary l i n e ana lys i s response to photosynthet i ca l ly act ive rad ia t ion (PAR) from second year needles for western hemlock seedlings i n dormancy induction treatments: 1) long-day dry (LDD), 2) long-day wet (LDW), 3) short-day dry (SDD), and 4) short-day wet (SDW). Figure 12. Net photosynthesis boundary l i n e ana lys i s response to vapour pressure d e f i c i t (VPD) from second year needles for western hemlock seedlings i n dormancy induct ion treatments: 1) long-day dry (LDD), 2) long-day wet (LDW), 3) short-day dry (SDD), and 4) short-day wet (SDW). 68 N E T P H O T O S Y N T H E S I S (/U mol m " 2 s " 1 ) 6 - i • 0 0 .5 1 1.5 2 PAR (mmol r r fV 1 ) N E T P H O T O S Y N T H E S I S fJJ. mo l m " 2 s " 1 ) 6 -5 -4 -3 -2 - L D D : -L D W : Y = 6 . 9 6 - 1.37x : r 2 = , 8 8 1 - S D D : " Y " - - e . 5 7 — • 1:21x:r- 2=-.72 S D W : Y = 6 . 5 0 - , 9 4 0 x : r 2 =.75 0 H 1 1 1 1 1 1 1 0 0 . 5 1 1.5 2 2 . 5 3 3 . 5 4 VPD (kPa) LDD — LDW SDD - - SDW 69 R-square v a l u e s f o r a l l DIT s e e d l i n g s were c a l c u l a t e d to be g r e a t e r than 0 . 90 . No d i f f e r e n c e s i n Pn response to v a r y i n g PAR were found from the second year n e e d l e s . Maximum Pn f o r second year needle response ( F i g . 11) i n c r e a s e d as compared to f i r s t year needles ( F i g . 5 ) , from 60% f o r SDD to 95% f o r LDW DIT s e e d l i n g s . A l i n e a r decrease i n Pn to i n c r e a s i n g VPD o c c u r r e d ( F i g . 12). Net p h o t o s y n t h e t i c response decreased from 50 to 66% i n a l l DIT from 0.5 to 3.8 kPa VPD l e v e l s , w h i le xylem p r e s s u r e p o t e n t i a l s were never l e s s than -1 . 0 MPa ( F i g . I E ) . A simple l i n e a r e q uation best r e l a t e d Pn to VPD. R-square v a l u e s were between 0.73 to 0.88. Short-day wet s e e d l i n g s had a g r e a t e r Pn at high VPD compared to other DIT. When compared to f i r s t year needles i n f i g u r e 6, i t can be seen t h a t second year needles show a h i g h e r Pn response at comparable v a l u e s . Surface response of Pn to v a r y i n g PAR and VPD f o r a l l fo u r DIT are shown i n f i g u r e s 13A-D. Pn response to PAR f o r any g i v e n VPD showed t h a t Pn was extremely r e s p o n s i v e to PAR -2 -1 up to 0.7 mmol m s . I n a d d i t i o n , Pn i s h i g h l y responsive to VPD at a l l l i g h t i n t e n s i t i e s . Again, due to model l i m i t a t i o n s of the model at v e r y low PAR, a l i g h t compensation p o i n t cannot be determined. The e q u a t i o n t h a t best d e s c r i b e d these v a r i a b l e s was i d e n t i c a l to the f i r s t year needle models, and i n c l u d e d the 70 Figure 13. Net photosynthesis (Pn) response to photosynthet ica l ly act ive rad ia t ion (PAR) and vapour pressure d e f i c i t (VPD) from second year needles of western hemlock for: A) long-day dry (LDD), B) long-day wet (LDW), C) short-day dry (SDD), and D) short-day wet (SDW). The regression models are as fol lows: LDD: Pn = 6.020 -0.828(PAR) +0.0143(1/PAR) +1.688(In(PAR)) -0.922(VPD): r = .72 LDW: Pn = 6.877 -1.050(PAR) +0.0176(1/PAR) +1.829(In(PAR)) -1.123(VPD): r = .83 SDD: Pn = 6.230 -1.052(PAR) +0.0171(1/PAR) +1.761(ln(PAR)) -0.860(VPD): r = .75 SDW: Pn = 6.711 -0.969(PAR) +0.0113(1/PAR) +1.785(In(PAR)) -0.976(VPD): r = .85 7 1 72 fo l lowing components: constant, PAR, inverse PAR, natural logarithm of PAR, and VPD. A l l components s i g n i f i c a n t l y contr ibuted to the model. R-square values are r e l a t i v e l y high ( 0 . 7 6 - 0 . 8 6 ) , and at tes t to the s ign i f i cance of PAR and VPD i n accounting for Pn v a r i a t i o n . At low VPD l eve l s (< 1 . 0 kPa), and at moderate to high - 2 - 1 PAR ( 0 . 7 - 2 . 2 mmol m s ), both non moisture stressed treatments had higher Pn than moisture stressed seedl ings . However, at high VPD (greater than 3 . 5 kPa) and a l l PAR l e v e l s , short-day seedlings maintained higher Pn rates than long-day seedl ings . Short-day wet seedlings had the highest o v e r a l l Pn performance of a l l DIT. 73 WESTERN RED CEDAR Environmental Conditions Predawn xylem water potentials measured monthly never were lower than -0.33 MPa (Table 5). The lowest s o i l water poten t i a l reading recorded for western red cedar sampling days was -0.11 MPa on August 22, 1988 (Table 1 ) . S o i l temperatures (-10 cm) were between 8 and 22°C (Table 5). Morphology data showed no blocking e f f e c t or blocking x treatment i n t e r a c t i o n at p=0.05 (unreported data). Thus, experimental and sampling errors were combined for a new error term for data analysis. Preplant Morphology Seedlings i n the LDW DIT had the greatest height, diameter, shoot dry weight and foliage surface area (Table 6 ) . Moisture stress DIT seedlings were smaller than non moisture stressed seedlings, but the differences were not s i g n i f i c a n t . Moisture stressed DIT seedlings had better shoot to root and seedling water balance r a t i o s . Morphology After One Growing Season Each DIT grew approximately 50 cm in height after 8 months on the controlled f i e l d s i t e (Table 6 ) . Shoot dry weights and diameters were not s i g n i f i c a n t l y d i f f e r e n t (p=0.05) between DIT. No foliage damage occurred after 8 months of growth. There were no s i g n i f i c a n t differences 74 TABLE 5. Predawn water potential of western red cedar from different dormancy induction treatments and s o i l temperature from stable environment data collection days. Dormancy Induction Treatment April 21 Predawn Water Hay 30 Potential June 29 (- MPa) July 18 + 1 S.E. Aug 22 Sept 29 LDD1' .13+.01a2) .28+.02a .31+.03a .17+.01b .18+.02b .15+.Ola LDW .15±.01a .22+.Ola .33+.05a •18±.02b .14+.Ola .14+.Ola SDD .15±.01a •29±.06a .28+.02a .15+.Ola .12+.Ola .14+.Ola SDW .14+.Ola .28±.03a .33+.02a .12+.02a .13+.Ola .11+.Ola Noon S o i l Temp, at -10cm (°C) 8 18 22 20 18 13 Long-day dry Long-day wet Short-day dry Short-day wet A difference in the letter within each date indicates a significant difference between dormancy induction treatments at p » 0.05 as determined by ANOVA and Waller-Duncan mean separation test. 1) LDD LDW SDD SDW Table 6. Morphological development of western red cedar seedlings from d i f f e r e n t dormancy induction treatments before f i e l d planting and after one growing season on a f i e l d s i t e . SHOOT ROOT SHOOT/ROOT RATIOS Dormancy Height Root Dry Foilage Foilage Container In S o i l Total Root Total Shoot Total Shoot Seedling Induction (cm) Collar Weight Surface Damage Plug Dry Dry Wt. Dry Wt. Surface Total Root New Roots Water Treatment Diameter (g) Area Index' 1 1 Wt. (g) (g) (9) Area (by Wt.) (by Wt.) Balance' 2 1 (cm) (cm2) (cm2) MARCH 15, 19 !8 -(Before Outplant) LDD<3> 29 46±.46b' 4 1 .28±.01a 1.66±.06b 252.0±7.2b 1.0o'5> .52±.03a - .52±.03a 123.5±9.2a 3.37±.14a - 12.20± .56a LDW 30 94+.54a .28+.Ola 2.00+..10a 323.6±14.6a 1.00 .54±.05a - .54±.05a 114.6±10.6a 4.17±.25bc - 15.33±1.16bc SDD 25 98±.46c .27±.01a 1.59±.06b 259.3±8.0b 1.00 .46±.03ab - .46±.03ab 112.5±8.4a 3.68±.19ab - 13.91± .83ab SDW 26 20+.61c .27±.01a 1.68±.09b 281.7±11.9b 1.00 .38±.03b - .38±.034b 99.0t7.1a 4.60±.21c - 17.67±1.04c en - NOVEMBER 15, 1988 -(8 Months After Outplant) LDD 77 50±3 30a 1 32± 03a 39 94+1 91a - 1 00(5) 4.91±.30a 6.06±.39a 10 97± 54a 3 66± 12a 6 72±.34a 2 77±.08a LDW 82 00±1 84a 1 40+ 05a 47 40+2 89a - 1 00 5.52±.31a 6.93±.66a 12 «± 92a - 3 87± 22a 7 08±.46a 2 79±.19a SDD 76 56+2 68b 1 34+ 05a 41 53±2 65a - 1 00 5.06+.41a 5.45±.41a 10 51± 74a - 3 98± 12a 7 76±.44a 2 99±.13a SDW 78 72±1 15a 1 44i 05a 47 39±2 46a - 1 00 5.93+.56a 6.17±.37a 12 10± 84a - 3 98± 19a 7 84±.50a 2 79+.16a (1) Needle damage index was catagorized as: 1=100*, 2=90-99%, 3=75-89%, 4=50-74%, 5=25-49%, and 6=1-24% green needles. (2) Seedling water balance ratio i s : shoot dry weight/(diameter x s o i l root dry weight). (3) LDD = Long-day dry LDW = Long-day wet SDD • Short-day dry SDW = Short-day wet (4) Mean and standard error. A difference in the l e t t e r for a morphological variable within each harvest date indicates a s i g n i f i c a n t difference between dormancy induction treatment at p = 0.05 as determined by ANOVA and Waller-Duncan mean separation test. (5) No s t a t i s t i c a l analysis due to lack of variation i n one or more treatments. 76 TABLE 7. Relative growth rate of western red cedar seedlings from different dormancy induction treatments for the f i r s t growing season on a moisture-controlled f i e l d site. Relative Growth Rates Dormancy Induction Treatment Height (cm/cm/mon.) Diameter (cm/cm/mon Shoot Dry Wt. •) (g/g/mon.) Total Root Dry Wt. (g/g/mon.) LDD1) .121 .194 .396 .381 LDW .122 .201 .396 .392 SDD .135 .200 .408 .391 SDW .138 .209 .417 .433 LDD = Long-day dry LDW = Long-day wet SDD = Short-day dry SDW = Short-day wet 77 between DIT for root dry weights or any of the measured shoot/root r a t i o s . Relat ive growth rates for height , diameter, shoot and root dry weight are found i n Table 7. Monthly Measurement of Repl icated P h y s i o l o g i c a l Data at Stable Environmental Condit ions Except for morning measurements i n May and June, PAR data showed a l l measurements were taken under c lear sunny skies ( F i g . 14A). Vapour pressure d e f i c i t range for data c o l l e c t i o n was moderate from 1.0 to 2 .5 kPa ( F i g . 14B). -2 -1 Maximum Pn was 2 .5 umol m s for f i r s t year fo l iage -2 -1 i n May, and 5.4 umol m s for second year fo l iage in August under s i m i l a r environmental condit ions ( F i g . 14C). On 2 of the 4 measurement occasions i n A p r i l and May ( f i r s t year fo l iage) moisture s tress DIT had s i g n i f i c a n t l y higher gwv readings ( F i g . 14D). LDD seedlings ranked f i r s t on 3 of the 4 occasions, while SDD seedlings ranked f i r s t on the other. Second year fo l iage gwv (June - September) exhibi ted no DIT or seasonal trends. From A p r i l to September a l l measured xylem water po tent ia l s (^x) were between -0 . 4 and - 0 . 8 MPa ( F i g . 14E). Pressure-volume analys i s taken monthly on LDW DIT had a minimum turgor loss point of -1.3 MPa (unpublished data) . Average <\>x for each DIT were s i m i l a r for most of the growing season. 78 Figure 14. Morning (Mn) and afternoon (Af) measurements taken each month across the growing season for: A) photosynthet ical ly act ive rad ia t ion (PAR), B) vapour pressure d e f i c i t (VPD), C) net photosynthesis (Pn), D) stomatal conductance (gwv), and E) xylem water po tent ia l x) for western red cedar seedlings from dormancy induct ion treatments: 1) long-day dry (LDD), 2) long-day wet (LDW), 3) short-day dry (SDD), and 4) short-day wet (SDW). S ign i f i cant di f ferences determined by ANOVA and Waller-Duncan mean separation test (p=0.05) are shown by d i f f erent l e t t e r s . Days with no l e t t e r i n g indicate no s t a t i s t i c a l l y s i g n i f i c a n t treatment d i f f erences . -1 I I I I I I I I I Mn Af Mn Af Mn Af Apr May Jun • LDD ESI LDW i i • Mn Af Mn Af Mn Af Jul Aug Sep SDD ^ SDW 80 P h y s i o l o g i c a l Response of F i r s t Year Fol iage As VPD l eve l s increased from 0.5-1.0 kPa, gwv rates decreased qu ick ly ( F i g . 15). For VPD values greater than l . O k P a , gwv showed a s l i g h t decrease as VPD increased. No evidence of stomatal c losure was found. The best equation descr ib ing the gwv to VPD data included VPD and inverse VPD. No constant was used in the equation, since i t d id not s i g n i f i c a n t l y contribute at p=0.05. R-square numbers have been adjusted for removal of the constant component. O v e r a l l , LDW seedlings had the lowest gwv response to changing VPD. Above 1.0 kPa, SDD seedlings maintained a 0.01 cm s~* greater gwv rate than SDW and LDD DIT seedl ings . For most of the VPD range, moisture stressed DIT seedlings maintained a higher gwv than the i r non moisture stressed DIT seedl ing counterparts . Stomatal conductance response showed an i n s e n s i t i v i t y -2 -1 to increas ing PAR from 0.10 to 2.2 mmol m s ( f u l l sunl ight) ( F i g . 16). There i s a s l i g h t increase i n gwv over th i s range re f l ec ted i n the p o s i t i v e PAR c o e f f i c i e n t s . A l i n e a r model was found to best represent the data. Both components, constant and PAR, s i g n i f i c a n t l y contributed to the equation. Even though the R-square values are low t h i s does not r e f l e c t the l i n e f i t , but more so the lack of a strong r e l a t i o n s h i p . Seedling DIT inf luenced gwv response to PAR. LDW seedlings had the lowest response over the ent i re PAR range. 81 Figure 15. Stomatal conductance boundary l i n e analys i s response to vapour pressure d e f i c i t (VPD) from f i r s t year needles for western red cedar seedlings i n dormancy induct ion treatments: 1) long-day dry (LDD), 2) long-day wet (LDW), 3) short-day dry (SDD), and 4) short-day wet (SDW). Figure 16. Stomatal conductance boundary l i n e ana lys i s response to photosynthet ica l ly act ive rad ia t ion (PAR) from f i r s t year needles for western red cedar seedlings i n dormancy induction treatments: 1) long-day dry (LDD), 2) long-day wet (LDW), 3) short-day dry (SDD), and 4) short-day wet (SDW). 82 S T O M A T A L C O N D U C T A N C E ( c m s " 1 ) 0.1 0 \\\ • \\ \\ ' • • \ \ L D D : Y = .0691 + . 0 8 8 0 x " V 2 =.80 L D W : Y = . 0 7 6 3 + . 0 6 8 6 x - 1 : r 2 = 8 7 S D D : Y = .1114 + . 0 4 4 7 x " 1 : r 2 =.57 S D W : Y = . 0 9 2 5 + . 0 5 7 9 x " V 2 =.73 0 0 . 5 1 1.5 2 2 .5 VPD (kPa) S T O M A T A L C O N D U C T A N C E ( c m s " 1 ) 0 .2 i 0 . 1 5 0.1 -L D D : Y = .146 + .010x : r 2 =.13 1 0 5 L D W : Y = .123 + ,017x : r 2 = . 2 4 S D D : Y = .128 + , 0 2 3 x :r 2 = . 3 4 S D W : Y = .140 + , 0 0 8 x : r 2 =.08 0 -I 1 1 1 r 0 0 .5 1 1.5 2 PAR (mmol m 2 s"1) L D D — L D W S D D - S D W 83 Moisture stressed DIT had a moderate a f fec t on gwv. Long-day dry seedlings were 0.01 to 0.02 cm s~* higher as compared to LDW seedlings for any PAR values . Short-day dry seedlings showed a higher response for the PAR range measured. The graphs i l l u s t r a t i n g gwv response to PAR and VPD for the four DIT are found in f igures 17A-D. A l l treatments showed a strong response to VPD below 1.0 kPa at a l l PAR. Beyond that po int , gwv leve led of f maintaining a nearly constant value up to 2.5 kPa. The highest gwv values for any segment of VPD were at high PAR. Response of gwv to PAR was a weak l i n e a r response across PAR values greater than 0.1 -2 -1 mmol m s . Data used for the gwv to VPD 2-dimensional (2-D) boundary l i n e analys i s were most l i k e l y c o l l e c t e d at high PAR l e v e l s . The modell ing equation which was used to best f i t the data for a l l treatments included a constant, PAR, and the inverse of VPD. Moderate R-square values (0.33 - 0.65) were computed. These values were a resu l t of combining a strong gwv to VPD r e l a t i o n s h i p ( F i g . 15), to a weak gwv to PAR r e l a t i o n s h i p ( F i g . 16). For environmental condit ions having VPD values less than 1.0 kPa, the 3-D response shows that LDD DIT seedlings had a s l i g h t l y higher gwv response at a l l PAR l e v e l s . When VPD values were between 1.0 and 2.5 kPa, moisture stressed DIT seedlings maintained higher gwv than t h e i r non moisture stressed seedl ing counterparts , e s p e c i a l l y at low PAR. The LDW DIT seedlings showed the lowest o v e r a l l gwv values over 84 Figure 17. Stomatal conductance (gwv) response to photosynthet ica l ly act ive rad ia t ion (PAR) and vapour pressure d e f i c i t (VPD) from f i r s t year needles of western red cedar for: A) long-day dry (LDD), B) long-day wet (LDW), C) short-day dry (SDD), and D) short-day wet (SDW). The regression modols are as fol lows: LDD: gwv = 0. 0449 + 0. 0100(PAR) + 0. 0661(1/VPD): 2 r 2 = .50 LDW: gwv = 0. 0112 + 0. 0204(PAR) + 0. 0627(1/VPD): 4 = .46 SDD: gwv = 0. 0691 + 0. 0055(PAR) + 0. 0374(1/VPD): z. r 2 = . 33 SDW: gwv = 0. 0187 + 0. 0175(PAR) + 0. 0701(1/VPD): r = .65 86 the environmental condit ions measured, whereas both water stressed treatments showed the highest va lues . It would appear that daylength had l i t t l e or no inf luence on gwv. Western red cedar seedl ing Pn rap id ly increased with -2 -1 PAR to 1.0 mmol m s and continued to increase but at a d iminishing rate up to f u l l sunl ight ( F i g . 1 8 ) . I t would appear that there i s no e a s i l y - d e f i n e d l i g h t saturat ion p o i n t . L ight compensation value was between 0.02 and 0.03 -2 -1 mmol m s (unreported data) . The equation used to best describe the data consisted of the fo l lowing components; constant, PAR, inverse PAR, and natura l log of PAR. Each component s i g n i f i c a n t l y contributed to the response model. For a l l treatments, R-square values were very high ranging from 0 . 9 4 - 0 . 9 6 . Both moisture stressed DIT seedlings had higher Pn response then t h e i r non moisture stressed seedl ing counterparts . Moisture stressed seedl ing response began to -2 -1 separate at approximately 0.2 mmol m s and maintained a -2 -1 0 . 1 - 0 . 3 yt/mol m s Pn rate d i f ference up to f u l l sun l ight . Daylength DIT had no inf luence on Pn versus PAR response, except at the highest PAR l e v e l s , LDW seedlings had a higher Pn than SDW seedl ings . The response to increas ing VPD ( 0 . 5 - 2 . 0 kPa) shows Pn decreasing l i n e a r l y with Pn rate d e c l i n i n g by 20-30% depending on DIT ( F i g . 19 ) . A l i n e a r equation best described the data with both components s i g n i f i c a n t l y contr ibut ing to the model. R-square 87 Figure 18. Net photosynthesis boundary l i n e ana lys i s response to photosynthet i ca l ly act ive rad ia t ion (PAR) from f i r s t year needles for western red cedar seedlings i n dormancy induct ion treatments: 1) long-day dry (LDD), 2) long-day wet (LDW), 3) short-day dry (SDD), and 4) short-day wet (SDW). Figure 19. Net photosynthesis boundary l i n e analys i s response to vapour pressure d e f i c i t (VPD) from f i r s t year needles for western red cedar seedlings in dormancy induct ion treatments: 1) long-day dry (LDD), 2) long-day wet (LDW), 3) short-day dry (SDD), and 4) short-day wet (SDW). 88 N E T P H O T O S Y N T H E S I S ( / u m o l r r f 2 s _ 1 ) 4 • — r r _ _ — — — / L D D : Y = = 3 . 8 8 - 4 9 4 x +.0118x~ 11.21lnx : r 2 =.96 1 L D W : Y = 3 . 2 3 - 1 8 0 x +.0115x~ 1+1.07lnx :r 2 =.95 / S D D : S D W : Y Y = 4.10 - , 731x + . 0 2 4 6 x _ l 1 . 4 1 l n x : r 2 = 3 . 3 0 - 3 2 4 x +.0119x" 1 +1.06lnx : =.94 r 2 = . 9 6 0 0 .5 1 1.5 2 PAR (mmol m"V1) N E T P H O T O S Y N T H E S I S (/U mo l m - 2 s " 1 ) 4 -3 -2 -L D D : Y = 4 . 2 3 - . 7 3 0 x : r 2 = . 4 8 1 - L D W •: - • Y -=• 4 •. 2 4 • ~ • .• 8 3 Ox- • :-r •2-=•. 4 2 S D D : Y = 4 . 7 5 - 1 .048x : r 2 = . 5 3 S D W : Y = 3 . 7 6 - . 6 5 6 x : r 2 = . 5 0 0 -I 1 1 1 1 ' 0 0 .5 1 1.5 2 2 .5 VPD (kPa) LDD — LDW SDD - - SDW 89 values for each DIT equation were moderate (0.42-0.53) . The R-square values are not seen as a lack of f i t , but a lack of a strong r e l a t i o n s h i p between Pn and VPD over the range of VPD l eve l s tes ted . Moisture stressed DIT seedlings exhibi ted higher Pn as compared to the non moisture stressed DIT seedl ings . SDD seedlings showed the best Pn response for VPD values less than 1.5 kPa, while LDD seedlings produced the highest values up to 2.3 kPa. Short-day wet seedlings showed the lowest Pn values over the VPD range measured. Surface response models of Pn to PAR and VPD leve l s showed that Pn was sens i t ive to both var iab le s ( F i g . 20A-D). Net photosynthesis was responsive to PAR changes from 0 to -2 -1 2.2 mmol m s with the greatest s e n s i t i v i t y up to 0.6 -2 -1 mmol m s and thereafter showing a p o s i t i v e but weaker response. Seedling Pn response to VPD showed a s i g n i f i c a n t l i n e a r response for a l l PAR values . Note that due to the nature of the equation se lec ted , l i g h t compensation point can not be determined from the graph. The equation which best described the data included the fo l lowing components; constant, inverse PAR, natura l log of PAR, PAR squared, and VPD. Note, th i s equation does not have a l i n e a r PAR term (non-s ign i f i cant at p=0.05), but includes a PAR square term. Each component of the equation contr ibutes s i g n i f i c a n t l y to the model (p - 0.05). R-square values are r e l a t i v e l y high (0.75 - 0.87) showing a strong r e l a t i o n s h i p of Pn to both PAR and VPD. 90 Figure 20. Net photosynthesis (Pn) response to photosynthet ica l ly act ive rad ia t ion (PAR) and vapour pressure d e f i c i t (VPD) from f i r s t year needles of western red cedar for: A) long-day dry (LDD), B) long-day wet (LDW), C) short-day dry (SDD), and D) short-day wet (SDW). The regression models are as fol lows: LDD: Pn = 3.479 +0.0125(1/PAR) +1.089(In(PAR) -0.168(PAR) 2 -0.699(VPD): r = .75 „ LDW: Pn = 2.894 +0.0032(1/PAR) +0.781(In(PAR) -0.044(PAR) -0.559(VPD): r = .77 SDD: Pn = 3.284 +0.0097(1/PAR) +1.014(In(PAR) -0.117(PAR) 2 -0.689(VPD): r = .76 , SDW: Pn = 2.960 +0.0048(1/PAR) +0.822(In(PAR) -0.064(PAR) Z -0.587(VPD): r = .87 91 92 Net photosynthesis response to PAR at low VPD exhibited very s i m i l a r DIT ranking and response as the 2-D boundary l i n e analysis (Fig. 18). Seedlings i n LDD, followed by SDD seedlings, showed the highest response followed by SDW and LDW. At the highest measured VPD l e v e l s , Pn response was si m i l a r for a l l DIT seedlings. Overall, LDD seedlings were best able to maintain a high l e v e l of Pn over the range of environmental conditions measured as compared to other DIT seedlings. Physiological Response of Second Year Foliage Stomatal conductance shows a c u r v i l i n e a r response to changing VPD, with a rapid decline i n gwv up to VPD values of 2.0 kPa (Fig. 21). Thereafter gwv exhibited a slow constant decline to 4.0 kPa. Second year foliage maintained a higher gwv at similar VPD as compared to f i r s t year f o l i a g e . Both foliage types were sensitive to VPD, but at d i f f e r e n t l e v e l s . Like f i r s t year foliage response, the best equation included VPD and inverse VPD. No constant was used since i t did not s i g n i f i c a n t l y contribute to the equation. As a r e s u l t , R-square values were adjusted. R-square values were moderate having values ranging from 0.60 to 0.81. No differences between DIT seedlings were observed for gwv at low to moderate VPD l e v e l s (1.0 - 3.0 kPa). At higher VPD l e v e l s (3 .0-4.0 kPa) gwv was s l i g h t l y higher for short-day as compared to long-day seedlings. 93 Figure 21. Stomatal conductance boundary l i n e analys i s response to vapour pressure d e f i c i t (VPD) from second year needles for western red cedar seedlings i n dormancy induct ion treatments: 1) long-day dry (LDD), 2) long-day wet (LDW), 3) short-day dry (SDD), and 4) short-day wet (SDW). Figure 22. Stomatal conductance boundary l i n e analys i s response to photosynthet i ca l ly act ive rad ia t ion (PAR) from second year needles for western red cedar seedlings in dormancy induction treatments: 1) long-day dry (LDD), 2) long-day wet (LDW), 3) short-day dry (SDD), and 4) short-day wet (SDW). 94 S T O M A T A L C O N D U C T A N C E ( c m s " 1 ) 0.2 0.1 \ \ L D D : Y = .b0889x + .320x"1:r2=.81 L D W : Y = .00854X + .323x _ l:r 2=.81 S D D : Y = ,01696x + ,279x-1:r-2=.60 S D W : Y - .01534x + ,302x"V 2=.69 0 0 1 2 3 4 VPD (kPa) S T O M A T A L C O N D U C T A N C E ( c m s " 1 ) 0 H 1 \ 1 r 0 0.5 1 1.5 2 PAR (mmol rrfV1) LDD — LDW SDD - - SDW 95 Stomatal conductance versus PAR showed a moderately strong r e l a t i o n s h i p ( F i g . 22). On average, gwv increased —1 —2 —1 —l 85%, from 0.13 cm s at 0.1 mmol m s to .24 cm s at -2 -1 2.1 mmol m s . Compared to f i r s t year fo l iage ( F i g . 16), —2 —1 no d i f ferences were observed at low PAR (0.1 mmol m s ); —2 —1 however, at high PAR l eve l s (2.1 mmol m s ) second year fo l iage had on average 40% greater gwv values . S t a t i s t i c a l l y , the best equation to describe the data was a l i n e a r model. R-square values of the l i n e a r model were between 0.56 and 0.74. Unl ike f i r s t year f o l i a g e , second year fo l iage of d i f f e r e n t DIT seedlings d id not influence gwv response to PAR. Figures 23A-D show the second year fo l iage response surface model of gwv to simultaneous changes in PAR and VPD for a l l dormancy induct ion treatments. For any PAR l e v e l , gwv i s responsive to VPD up to 1.5 kPa. Thereafter depending on l i g h t l e v e l s , gwv was r e l a t i v e l y constant with only a gradual decrease. No evidence of stomatal c losure was found up to the maximum measured VPD l e v e l (4.0 kPa). With increas ing PAR, gwv exhibi ted a l i n e a r response up to -2 -1 approximately 1.5 mmol m s , and thereafter maintained a constant or decreasing trend depending on DIT. The best equation included the fo l lowing components; PAR, natura l log of PAR, PAR squared, and inverse VPD. A l l components s i g n i f i c a n t l y contributed to the model. A constant component was not s i g n i f i c a n t , and thus R-square 96 Figure 23. Stomatal conductance (gwv) response to photosynthet ica l ly act ive rad ia t ion (PAR) and vapour pressure d e f i c i t (VPD) from second year needles of western red cedar for: A) long-day dry (LDD), B) long-day wet (LDW), C) short-day dry (SDD), and D) short-day wet (SDW). The regression models are as fol lows: LDD: gwv = 0.145(PAR) -0.0169(In(PAR) -0.0429(PAR) 2 +0.0668(1/VPD): r = .29 „ LDW: gwv - 0.127(PAR) -0.0118(In(PAR) -0.0330(PAR) +0.0688(1/VPD): r = .32 SDD: gwv = 0.121(PAR) -0.0229(In(PAR) -0.0285(PAR) +0.0616(1/VPD): r = .21 „ SDW: gwv = 0.160(PAR) -0.0222(ln(PAR) -0.0467(PAR) +0.0474(1/VPD): r = .22 97 98 values were adjusted. R-square values were low ( 0 . 2 1 - 0 . 3 2 ) probably r e f l e c t i n g the large f l a t area for environmental condit ions where gwv readings were r e l a t i v e l y constant (VPD values greater than 1 . 5 kPa and PAR values greater than 0 . 1 mmol m _ z s-^") . The moisture stressed seedlings were able to maintain a _2 constant l e v e l of gwv at values greater than 1 . 5 mmol m s - * whereas non moisture stressed seedlings showed a decrease i n gwv, p a r t i c u l a r l y at high VPD. Otherwise d i f ferences between DIT were minor. Net photosynthesis for a l l seedlings rose r a p i d l y up to - 2 - 1 0 . 3 mmol m s and then increased l i n e a r l y with increas ing l i g h t i n t e n s i t y ( F i g . 2 4 ) . F i r s t year fo l iage 2 -D responses ( F i g . 1 8 ) are very s imi lar to second year fo l iage up to 0 . 5 - 2 - 1 mmol m s . Thereafter , f i r s t year fo l iage begins to show diminish ing Pn with increas ing PAR; whereas, second year fo l iage maintains a l i n e a r Pn increase with increas ing PAR - 2 - 1 - 2 - 1 up to a rate of 5 . 9 //mol m s at 2 . 1 mmol m s Measurements at f u l l sunl ight produced the greatest r e l a t i v e d i f ference (60%) between f i r s t year ( F i g . 1 8 ) and second year fo l iage ( F i g . 2 4 ) . L ight compensation point of 0 . 0 2 -- 2 - 1 0 . 0 3 mmol m s d id not change from that obtained with f i r s t year fo l iage (unreported data) . The model that best described the data included a constant, PAR, and natural log of PAR. A l l equation components contributed s i g n i f i c a n t l y to the model. R-square values were very high ranging from 0 . 9 4 'to 0 . 9 6 . 99 Figure 24. Net photosynthesis boundary l i n e ana lys i s response to photosynthet i ca l ly act ive rad ia t ion (PAR) from second year needles for western red cedar seedlings i n dormancy induction treatments: 1) long-day dry (LDD), 2) long-day wet (LDW), 3) short-day dry (SDD), and 4) short-day wet (SDW). Figure 25. Net photosynthesis boundary l i n e analys i s response to vapour pressure d e f i c i t (VPD) from second year needles for western red cedar seedlings i n dormancy induct ion treatments: 1) long-day dry (LDD), 2) long-day wet (LDW), 3) short-day dry (SDD), and 4) short-day wet (SDW). 1 0 0 N E T P H O T O S Y N T H E S I S (/umol m ' 2 s 2 0 0 .5 1 • 1.5 PAR (mmol m'V1) N E T P H O T O S Y N T H E S I S (/U mol m" 2s" 1) 7 6 5 -4 -3 2 1 .LDD. : . Y . .=..8,0.5..-. 1,81.x.;r.2..=,8.6.. L D W : Y = 8 . 5 6 - 1.95x : r 2 = 9 4 -SDD-:-•¥•-=• 7-. 8 9 — -1; 77-x • :r- 2 - , 8 0 S D W : Y - 7 . 2 0 - 1.42x : r 2 =.57 1 VPD (kPa) LDD LDW SDD - SDW 101 No di f ferences i n Pn response to PAR between DIT were detected. The r e l a t i o n s h i p of Pn versus VPD i s seen i n f igure 25. The resu l t s show strong l i n e a r decrease i n Pn (from 5 . 9 to -2 - 1 1 . 9 //mol m s ) with increas ing VPD (from 1 . 0 to 3 . 8 kPa) producing an average decrease of 66% for a l l DIT. Note, the strong response occurred while plant moisture s tress was never lower than - 1 . 0 MPa during measurement. For both f i r s t year and second f o l i a g e , the rate of decrease was approximately the same. Net photosynthesis was best re la ted to VPD using a simple l i n e a r regress ion . Both components contributed s i g n i f i c a n t l y to the equation. R-square values were moderately high ranging from 0 .57 to 0 . 9 4 . Second year fo l iage showed no di f ferences between DIT seedlings Pn response to VPD. Response surface models of second year fo l iage Pn to combined PAR and VPD changes for a l l treatments are found in Figures 26A-D. At a l l l eve l s of PAR, Pn decreased l i n e a r l y with increas ing VPD. Note that at high VPD values the model showed no photosynthesis occurr ing at low l i g h t l eve l s (0 --2 - 1 0 .2 mmol m s ). Photosynthesis increased dramat ica l ly with i n i t i a l PAR leve l s and showed less of a response as PAR increased to f u l l sun l ight . Depending on the treatment, i t was a lso observed that Pn was s l i g h t l y i n h i b i t e d at PAR values approaching f u l l sun l igh t . Net photosynthesis response to PAR i s not exact ly the same as represented in 1 0 2 Figure 26. Net photosynthesis (Pn) response to photosynthet ica l ly act ive rad ia t ion (PAR) and vapour pressure d e f i c i t (VPD) from second year needles of western red cedar for: A) long-day dry (LDD), B) long-day wet (LDW), C) short-day dry (SDD), and D) short-day wet (SDW). The regression models are as fol lows: LDD: Pn = 2.097 +2.566(PAR) +0.532(In(PAR) -0 .741(PAR) 2 -0.600(VPD): r = .69 LDW: Pn = 1.818 +3.345(PAR) +0.417(In(PAR) -0.980(PAR) Z -0.721(VPD): r = .66 SDD: Pn = 2.557 +1.740(PAR) +0.664(In(PAR) -0.425(PAR) Z -0.668(VPD): r = .68 SDW: Pn = 1.364 +3.750(PAR) +0.376(In(PAR) -1.188(PAR) -0.550(VPD): r . .66 103 104 the 2-D graph ( F i g . 24). Although they are s i m i l a r , the d i f ference i s due to the analys i s procedure for the 2-D graph. The equation which best modelled Pn to PAR and VPD inc ludes : constant, PAR, natural log of PAR, PAR squared, and VPD. Each component was s i g n i f i c a n t (p=0.05). R-square values range from 0.66 to 0 . 69 . Simi lar to the gwv 3-D response graphs, moisture stressed seedlings were able to maintain a constant or -2 -1 increas ing Pn at PAR leve l s above 1.5 mmol m s , while non moisture stressed seedlings showed a dec l ine i n Pn. Otherwise, a l l treatments showed s i m i l a r response for a l l other areas of the environmental matrix measured. 105 DISCUSSION There are numerous factors which must be considered when assessing the e f fec t c u l t u r a l treatments have on seedl ing growth and s u r v i v a l on a re fores ta t ion s i t e . Tree seedlings are l inked to t h e i r atmospheric environment by gas exchange through stomata. Hence, stomatal contro l of water loss and CO2 uptake are of considerable importance i n determining the capacity of seedlings to develop on a p a r t i c u l a r s i t e (Osonubi and Davies 1980a). In th i s research study the t e s t ing of the hypothesis , "do d i f f e r e n t stocktypes have d i f f e r e n t gas exchange responses to atmospheric condit ions?", was approached three ways: (1) r e p l i c a t e d measurements at stable environmental condi t ions , (2) p h y s i o l o g i c a l response to one increas ing environmental v a r i a b l e using boundary l i n e a n a l y s i s , and (3) p h y s i o l o g i c a l response surface to two simultaneously changing environmental v a r i a b l e s . F i r s t , morphology resu l t s for both species w i l l be discussed. Morphological Response of Western Hemlock I n i t i a l shoot dry weight of the LDW DIT was s i g n i f i c a n t l y higher than the LDD, SDD, SDW treatments. Shoot dry weights af ter one year growth were not s i g n i f i c a n t l y d i f f e r e n t . Reduced treatment di f ferences was shown i n a higher shoot dry weight r e l a t i v e growth rate (RGR) for LDD, SDD, and SDW seedlings as compared to the 1 0 6 LDW seedl ings . Greater growth by LDD, SDW, and SDD than LDW could poss ib ly be a r e f l e c t i o n of f i r s t year fo l iage higher net photosynthesis (Pn) response rate to photosy the t i ca l ly act ive r a d i a t i o n (PAR) ( F i g . 2) and vapour pressure d e f i c i t (VPD) ( F i g . 3). F i n a l average shoot heights were highest for the long-day seedlings (Table 3), however short-day seedlings showed greater height RGR (Table 4). The more balanced, p h y s i o l o g i c a l l y modif ied, seedlings were qu ick ly approaching the same s ize as the LDW seedlings which had begun with the larges t needle area and dry weight. S imi lar to these r e s u l t s , O ' R e i l l y (Pers. Comm.) studying the same stocktypes planted on a re fores ta t ion s i t e on Vancouver Is land found the long-day treatments to have the greatest height and diameter at the end of the f i r s t growing season. Long-day seedlings had the greatest f i n a l t o t a l root dry weight, r e f l e c t i n g the adjustment required to reach a shoot to root balance. In p a r t i c u l a r , the adjustment was more pronounced with LDD seedl ings , since they s tarted with the lowest root dry weight and highest seedl ing water balance r a t i o . Seedling treatments grown on a high ava i lab le s o i l moisture s i t e , when compared to the same seedl ing treatments planted on a re fores ta t ion s i t e grown for 8 months (data in Grossnickle et a l . 1990b), exhibi ted large morphological d i f f erences . Seedling growth on the high ava i lab le s o i l moisture s i t e showed, on average, 3 times the height and 107 root dry weight and 6 times the diameter and shoot dry weight as compared to those on the re fores ta t ion s i t e . Large d i f ferences i n growth were probably due, i n large par t , to lack of drought and weed competition on the contro l s i t e . As for stocktype e f fect on a coastal re fores ta t ion s i t e , the short-day seedlings showed the best response, a f ter one year growth, by having the lowest needle damage and best seedl ing water balance, and the best growth as shown by the number of stem uni ts per centimeter on the leader (Grossnickle et a l . 1990b). Calcu lated RGR over the same period on the re fores ta t ion s i t e showed that LDD, SDD, and SDW seedlings had the highest height , diameter, and shoot dry weight RGR values (unreported data) . Morphological Response of Western Red Cedar The LDW DIT (control) seedlings were not iceably larger p r i o r to f i e l d p lant ing (Table 6) . Af ter the eight month growing season, there were no s i g n i f i c a n t d i f ferences in seedl ing morphology among stocktypes. A poss ib le reason the i n i t i a l morphological d i f ferences were reduced, i s the s l i g h t l y higher Pn response to PAR and VPD from f i r s t year fo l iage of moisture stressed seedl ings . Seedlings from the contro l s i t e exh ib i t ed , on average 5.5, times the height , diameter and root dry weight growth, and 15 times the shoot dry weight growth as compared to s i m i l a r treatments on the re fores ta t ion s i t e (Unreported data) . I t i s noteworthy that western red cedar seedlings 108 exhib i ted remarkable growth, showing a 25- fo ld increase in shoot dry weight compared to an average 14-fo ld increase for western hemlock. This species d i f ference could poss ib ly r e s u l t from the non saturat ing Pn response to PAR (of the second year needles) of western red cedar as compared to a sa turat ing i rrad iance response for western hemlock. For western red cedar, daylength had a n e g l i g i b l e e f fec t on gas exchange, and marginal e f fec t morphological ly , perhaps because western red cedar do not develop a true bud (Hosie 1979). Moisture s tress showed a p o s i t i v e , yet marginal , e f fect p h y s i o l o g i c a l l y , and i t has been suggested that i t s ' b e n e f i c i a l e f fect may be improved by increas ing the moisture s tress l eve l s used to precondi t ion the seedlings (Grossnickle and Arnott Pers. Comm.). It therefore can be seen from th i s study that moisture s tress i s a more e f f ec t ive precondi t ioning treatment, as compared to daylength, for balanced shoot / root ra t io s and that more research into stronger stresses may prove f r u i t f u l . P h y s i o l o g i c a l Measurements at Stable Environmental  Condit ions This procedure attempted to c o l l e c t monthly measurements of r ep l i ca ted p h y s i o l o g i c a l data at stable environmental condit ions (western hemlock F i g . 1, western red cedar F i g . 14). I t was thought that th i s procedure would provide a method to monitor changes i n stocktype physiology over the f i r s t growing season. As response data, developed 109 l a t e r , ind icated (western hemlock F ig 2-13, western red cedar F i g . 15-26), the p h y s i o l o g i c a l i n t e r p r e t a t i o n could change dramat i ca l l y , depending on the environmental condit ions under which the data was c o l l e c t e d . Hence, environmental changes during measurement could confound stocktype p h y s i o l o g i c a l d i f f erences . In the f i e l d , i t was d i f f i c u l t to measure 40 seedlings (10 r e p l i c a t e s per treatment) i n 60 to 80 minute period and have c l i m a t i c condit ions constant throughout th i s time p e r i o d . Every e f f o r t was made to c o l l e c t data under c lear skies and th i s object ive was achieved for afternoon readings. Clear skies kept PAR and VPD v a r i a t i o n s , for the most p a r t , to a minimum. Under cloudy sk ies , c o l l e c t i n g data was more d i f f i c u l t because of c o n t i n u a l l y changing condi t ions , and th i s meant that data c o l l e c t i o n was d isrupted due to wide PAR v a r i a t i o n s which extended the sampling per iod , and increased VPD v a r i a t i o n s . Repl icated measurements method of data analys i s has been used i n contro l l ed environments (Blake 1983), on c h a r a c t e r i z i n g species d i f ferences (Running 1976, Fry and P h i l l i p s 1977), or comparing values at d i f f e r e n t dates (Running 1980). Grossnickle et a l . (1990b) used th i s method for data c o l l e c t e d on a re fores ta t ion s i t e with these same stocktypes, but found non-consistent trends. In further ana lys i s Grossnickle and Arnott (1990) used boundary l i n e a n a l y s i s , and judged th i s method better to separate stocktype d i f ferences because each data point was 110 independent with i t s own c l i m a t i c information, and thus was a better measure of p h y s i o l o g i c a l response. For the aforementioned reasons i t i s inherent ly d i f f i c u l t to d i scern true d i f ferences between stocktypes i n the f i e l d using r e p l i c a t e d measurements. It would appear that data c o l l e c t i o n , of th i s nature, should be obtained i n a c o n t r o l l e d environment for more r e l i a b l e r e s u l t s . Seedlings could be planted i n water permeable pots i n the f i e l d and moved into a contro l l ed environment the day before measurements were to be taken. Data could be c o l l e c t e d at an e f f ec t ive predetermined stable and constant environment and then seedlings taken back to the f i e l d . This could most l i k e l y be done over the growing season with minimal disturbance to the seedl ings . P h y s i o l o g i c a l Response: One Environmental Var iab le Basic Physiology Stomatal conductance (gwv) values of 0.1-0.3 cm s - *, determined from th i s study are comparable to other studies for western hemlock (Running 1976, L iv ings ton and Black 1987). No such data have been published for western red cedar by which to compare values . Stomatal response to increas ing VPD and/or PAR for these species have not been prev ious ly reported i n the l i t e r a t u r e , except for a re la t ive gwv term for western hemlock (Liv ingston and Black 1987). The decreasing c u r v i l i n e a r response to increas ing VPD i s I l l s i m i l a r to that observed for most coni fers species (Sandford and J a r v i s 1986, J a r v i s 1980). Xylem water po tent ia l s were always higher than -1.0 MPa and minimum turgor loss point was approximately -1.3 MPa, hence d e c l i n i n g gwv with increas ing VPD i s thought to be a feedforward stomatal response. In a feedforward system, stomata respond to atmospheric drought by d i r e c t drying of guard and epidermal c e l l s , even though seedl ing water p o t e n t i a l i s wel l above turgor loss point (Schulze et a l . 1987). Stomatal response to humidity can be independent of changes in bulk l ea f water p o t e n t i a l (Schulze and Kuppers 1979). Mechanics of a d i r e c t stomatal response to humidity i s a property of the epidermis, and i s re la ted to i t s steady state turgor (Losch 1977). Lange et a l . (1971) suggested that an equ i l ibr ium between epidermal water uptake from the mesophyll and a c u t i c l e t r a n s p i r a t i o n (determined by VPD) corresponds to a c e r t a i n stomatal aperture . Exact mechanisms w i l l remain unclear u n t i l more i s known about the needle water movement pathway (Schulze 1986b). Stomatal response to increas ing PAR showed gwv increas ing as PAR increased ( i . e . F i g . 3) . Research conducted on several coni fer species has shown that stomatal opening i n response to l i g h t exhibi ted two phases: f i r s t , a rapid increase i n gwv over low PAR l eve l s and, second, a very gradual increase of gwv over higher PAR l eve l s e . g . , Picea engelmannii (Kaufmann 1976), Pinus s y l v e s t r i s (Jarv i s 112 1980), and Abies las iocarpa (Kaufmann 1982a). The low l i g h t l e v e l response has been obscured by the boundary l i n e analys i s method ( i . e . F i g . 3), but i s seen i n 3-dimensional (3-D) surface response graphs ( i . e . F i g . 4A-D). Research has shown that two photoreceptors, blue and red l i g h t pigments, are involved i n stomatal opening with blue l i g h t important for low l i g h t l e v e l response and red l i g h t important at high l i g h t i n t e n s i t y (Zeiger 1 9 8 3 ) . Chlorophy l l i s accepted as the red photoactive pigment and f l a v i n as the blue photoactive pigment but the exact mechanism causing stomatal opening i s unknown (Ogawa et a l . 1978). It i s hypothesized that blue l i g h t functions as a switch to s t a r t stomatal opening, causing protons to be pumped into the guard c e l l s (Zeiger 1983). Measurements of Pn for western hemlock, other than Grossnickle et a l . (1988, 1990a, 1990b) and Grossnickle and Arnott ( 1 9 9 0 ) , have been documented i n a drought study by Br ix (1979) (rates were in d i f f i c u l t to convert u n i t s , mg CO2 hr~* dm -*) and Fry and P h i l l i p s (1977). There are no reported studies on Pn of western red cedar. Carbon dioxide a s s i m i l a t i o n increased i n an asymptotic manner, with increas ing l i g h t i n t e n s i t y for a l l four stocktypes s imi lar to other tree species (Beadle et a l . 1985b, Vu et a l . 1986). -2 -1 The l i g h t saturat ion range of 0 . 6 - 0.8 mmol m s has not been reported for western hemlock, but was s imi lar to sa turat ion l eve l s reported for other c o n i f e r s , e .g . Picea 113 s i t chens i s (Bong.) C a r r . (Beadle et a l . 1985a), Pinus teada (Teskey et a l . 1986) . Western red cedar f i r s t year fo l iage also had a sa turat ing i rrad iance for Pn ( F i g . 18) ; however, the second year fo l iage showed no saturat ing i rrad iance l e v e l ( F i g . 24). Lar ix l e p t o l e p i s also exhibi ted a non saturat ing type of response (Fry and P h i l l i p s 1976) , as wel l as Pinus  s y l v e s t r i s at moderate to high a i r temperatures (Beadle et a l . 1985a) . F i r s t year fo l iage showed a saturat ing i rrad iance poss ib ly because seedlings were grown i n high densi ty styroblocks which led to "shade" fo l iage development. On the contro l s i t e , fo l iage was developed i n an open area which allowed for "sun" fo l iage development. Sun fo l iage i s general ly th icker and has a higher Pn response to PAR as compared to shade fo l iage (Leverenz and J a r v i s 1979, Benecke et a l . 1981). Beadle et a l . (1985a) suggested that non saturat ing response i s re la ted to large gradients of l i g h t wi th in needles r e s u l t i n g from predominantly u n i d i r e c t i o n a l i l l u m i n a t i o n i n the f i e l d from the sun, and that thick needles would not have a l l react ion centers saturated at the same inc ident PAR, as in th in leaves . Hence, i t i s poss ib le that second year fo l iage Pn increased with increas ing PAR because, once the top of the th icker fo l iage was saturated, the bottom part continued to contribute to fo l iage Pn u n t i l i t reached a l i g h t saturat ion l e v e l . 114 The f ind ing that second year fo l iage of western hemlock had a lower saturat ing i rrad iance for Pn, and a greater Pn e f f i c i e n c y at low irradiance as compared to western red cedar i s consistent with the known high degree of shade tolerance of Tsuga species (Hosie 1979). Net photosynthesis reduction with increas ing VPD was observed for both species , and for both f i r s t year and second year needles. Net photosynthesis reduction i s not thought to be induced by lowering i n t e r n a l CO^ (Ci) (via stomatal c l o s u r e ) , but by t r a n s p i r a t i o n s tress (Sharkey 1984). D irec t measurements of Ci (Sharkey et a l . 1982) have revealed that Ci remains constant during various p h y s i o l o g i c a l stresses (Sharkey 1984, Briggs et a l . 1986, Scarascia-Mugnozza et a l . 1986). Calculated Ci values showed between 250 - 350 ppm for the ent ire study (unreported data) . Sharkey (1984) found that high t r a n s p i r a t i o n produced water stress over small areas within a l ea f and reduced mesophyll Pn. He proposed that large water po tent ia l gradients wi th in l ea f areo les , between the xylem and s i t e of evaporat ion, are responsible for Pn dec l ine observed after t r a n s p i r a t i o n s t re s s . The l i m i t a t i o n i s considered to be a t t r i b u t e d to reduced r ibulose-1 ,5-bisphosphate regeneration capaci ty at the mesophyll (Farquhar and von Caemmerer 1982), and/or losses i n ch loroplas t capacity to f ix CC>2 (Sharp and Boyer 1986). 115 Stocktype E f f e c t I t was found that greenhouse c u l t u r a l treatments af fected both the gwv and Pn response of western hemlock and western red cedar f i r s t year needles. In western hemlock, the short-day seedlings had a higher gwv response to increas ing PAR ( F i g . 2) and to increas ing VPD ( F i g . 3) . The explanation may be a t t r i b u t e d to one, or a l l three , of the fo l lowing poss ible- f a c t o r s . Grossnickle et a l . (1990a) working with the same stocktypes found that at low root temperatures, long-day seedlings had s i g n i f i c a n t l y higher res is tance to water movement as compared to short-day seedlings through the plant-atmosphere continuum. If res is tance d i f ference inf luenced gwv, i t i s thought that i t would most probably be through a minor feedback response. A second explanation i s through morphological modi f icat ion of stomata or p h y s i o l o g i c a l response modi f icat ion of the epidermis and guard c e l l s (feedforward system). Subtle d i f ferences i n c u t i c l e thickness could inf luence th i s response. T h i r d l y , perhaps a modi f icat ion of the feedforward system tolerance to evaporative demand was better developed i n the short-day seedl ings . It was found that the short-day seedlings had a lower osmotic p o t e n t i a l at saturated, and at turgor loss point water p o t e n t i a l , as compared to long-day seedlings just before f i e l d p lant ing (Grossnickle et a l . 1990a) . For western hemlock, moisture stress and daylength greenhouse c u l t u r a l treatments have an independent, and 116 combined, inf luence on Pn response to increas ing PAR. Moisture stressed seedlings had equal or higher Pn response p a r t i c u l a r l y at greater PAR than non moisture stressed seedl ings . Moisture stress precondi t ioning has been reported to p o s i t i v e l y inf luence other plant species ' Pn by poss ib ly decreasing non stomatal mesophyll l i m i t a t i o n s (Matthews and Boyer 1984, Sen Gupta et a l . 1989). For western hemlock, short-day seedlings exhibi ted a higher Pn response than d id long-day seedlings ( F i g . 5). S e i l o r and Johnson (1985) c i t e d i f ferences in osmotic p o t e n t i a l , as found i n western hemlock daylength treatments, could inf luence Pn response. A l s o , short-day treatments have a lower res istance to water movement along with better shoot to root ra t io s which may contribute to better water a v a i l a b i l i t y at the mesophyll (Grossnickle et a l . 1990a). Western red cedar f i r s t year needles moisture stressed seedlings had a higher Pn response to changing VPD. Again , decreased non stomatal l i m i t a t i o n of moisture stressed seedlings might contribute to th i s response (Matthews and Boyer 1984). A d d i t i o n a l l y , the osmotic p o t e n t i a l for western red cedar moisture stressed seedlings was marginal ly lower, as compared to non moisture stressed seedlings p r i o r to f i e l d p lant ing (Grossnickle et a l . 1988). For western hemlock, i t was i n t e r e s t i n g af ter observing the higher gwv to VPD response of short-day as compared to long-day, not to see SDW with as high Pn response as SDD seedl ings . This i s most l i k e l y due to the independent nature 117 of Pn and gwv (Kuppers and Schulze 1 9 8 5 ) , and the higher Pn response of moisture stress as compared to non moisture stressed seedl ings . Western hemlock LDD seedlings did not have a higher Pn response than might be expected, poss ib ly because the shoot to root imbalance, or higher seedling water res istance countered the moisture s tress treatment advantage. For both species , c u l t u r a l treatment e f fec t d id not manifest i t s e l f i n Pn response of second year fo l iage ( F i g . 1 1 , 2 4 ) . It seems reasonable that new f o l i a g e , developed in the same environment with no s o i l water r e s t r i c t i o n s , would have s i m i l a r mesophyll arch i tec ture and hence Pn response to increas ing PAR. Stomatal response of second year needles, however, showed a much reduced, but not iceable , treatment d i f f erence . It i s poss ib le that for western hemlock greenhouse c u l t u r a l DIT d i f ferences continued to influence gwv response through d i f ferences i n shoot to root r a t i o . This was not seen with western red cedar second year fo l iage probably because i n i t i a l western red cedar DIT morphologies were s i m i l a r . P h y s i o l o g i c a l Response: Two Environmental Var iab les Three dimensional models are a ser ies of 2-D models which show important in terac t ions of two v a r i a b l e s . For example, Pn to increas ing PAR 2-D f igure does not show the poss ib le e f fect VPD has on Pn over the ent i re PAR range. Likewise , second year gwv response to VPD 2-D f igure does 118 not show the gwv dec l ine that occurs at high VPD over the range of PAR. Development of 3-D phenomenological models descr ib ing gwv and Pn, using primary environmental fac tors , helps to further define gas exchange processes. For these reasons, gwv and Pn response surfaces were modelled to PAR and VPD. It became apparent from the 2-D graphs that large d i f ferences between stocktypes would not be d iscerned, but that small d i f ferences i n magnitude would have to be detected. Knowing the 2-D response type, a number of d i f f e r e n t empir ica l models were tes ted . One input environmental var iab le p h y s i o l o g i c a l response models are more numerous than simultaneously changing two input response models. Authors who have modelled the e f fects of simultaneously changing PAR and VPD on tree species are Grossnickle and Reid (1985) on Picea engelmannii for gwv and Meinzer (1982c) on Pseudotsuga menzies i i for water use e f f i c i e n c y . These response surfaces showed that gwv i s s trongly inf luenced by VPD and that PAR only has a modifying e f f e c t . Net photosynthesis versus PAR and VPD response surfaces show that l i g h t i n t e n s i t y i s the dominant f a c t o r , and that VPD has a strong modifying e f f e c t . Photosynthesis under most condit ions responds exponent ia l ly to increased PAR, and then l e v e l s o f f at a saturat ion l e v e l (western red cedar second year needles were an except ion) . increas ing VPD decreased the magnitude of th i s response. A representat ion of th i s 119 type has not been published for any forest tree species . However, i t i s noted that Meinzer (1982c) used th i s type of representat ion for Pseudotsuga menziesi i water use e f f i c i e n c y . The 3-D response surfaces indicated an independent behavior of gwv and Pn. When gwv was reduced dramat ica l ly by increas ing VPD, Pn was reduced only progres s ive ly . When gwv -2 -1 opened at low PAR (< 0.1 mmol m s ) to a near maximum, Pn -2 -1 d id not reach f u l l capacity u n t i l 0.6 - 0.8 mmol m s or more. Recent f indings describe the r e l a t i o n s h i p between Pn and gwv as independent, except under extreme condit ions (Beadle et a l . 1985a, Kuppers and Schulze 1985). Unique species d i f ferences were observed. Western hemlock second year fo l iage showed the t y p i c a l gwv reduction with low to moderate VPD (1.0 - 2.0) with gwv near zero at VPD l eve l s above 3.5 kPa. Since water potent ia l s (<Px) were above turgor l o s s , i t i s f e l t that th i s species exhibi ted a drought avoidant response ( L e v i t t '1972). Western red cedar second year fo l iage a lso had a reduced gwv at mild to moderate VPD, but had gwv values of approximately 0.1 cm s~* at a VPD of 4 .0 kPa and may be defined as a drought to lerant response ( L e v i t t 1972). Stocktype 3-D surface response d i f ferences were consistent with the 2-D responses. Upon close examination, western hemlock LDD, SDD, and SDW DIT f i r s t year needles had the highest Pn response, i n p a r t i c u l a r , SDD seedl ings . For western red cedar f i r s t year f o l i a g e , moisture stressed 120 seedlings had the highest Pn response. For both species, second year fo l iage of various stocktypes showed almost i d e n t i c a l Pn response. Whether a higher or lower gwv i s better under test condit ions remains unclear . It would seem that a higher gwv would be better for optimum Pn; however, these parameters for the most part are unre lated , except under extreme condit ions (Beadle et a l . 1985a). Perhaps a lower gwv would be better to conserve s o i l water, but r e a l i s t i c a l l y , th i s i s of l i t t l e consequence on a coastal r e fores ta t ion s i t e throughout most of the year. If one species does not use the water, another adjacent competing species w i l l use the water. The important factor i s to keep the stomata open as long as poss ib le under water stressed condi t ions , up to moderately dry cond i t ion , p a r t i c u l a r l y i n the f i r s t year of establishment. Open stomata are necessary for new root growth because current year photosynthate i s necessary for new root development (v. d. Driessche 1987). Perhaps the higher gwv under moderate V P D , are i n d i c a t i v e of moisture s tress to lerance . The western hemlock short-day seedlings had the greatest gwv response to high VPD l e v e l s , and also had the highest Pn and gwv response when drought tested up to -1.8 MPa predawn water po tent ia l p r i o r to f i e l d p lant ing (Grossnickle et a l . 1990a). 121 Advantages and Limi ta t ions of Phenomenological Models Two and three dimensional empir ica l models were constructed dep ic t ing gwv and Pn response to VPD and PAR. Advantages of using phenomenological models to various other types of p h y s i o l o g i c a l analys i s are described below. Two-dimensional models enable the e f fec ts of s ingle environmental factors to be separated. Factors such as optimum temperatures (Beadle et a l . 1985a), VPD and PAR (Jarv i s 1976) have been studied by th i s method. Empir ica l models are r e l a t i v e l y easy to create , and do not require complete understanding of biochemical mechanisms involved in the parameters measured (Hal l 1982). The 2-D models enable species , stocktype, and poss ib ly genotypic comparisons, without having to test the seedlings at the exact same time or environment, because a l l recorded data are treated independently. The developed equation can also serve to ca lcu la te response given c l i m a t i c input . Equations have been used for a number of studies (Kuppers and Schulze 1985, Thompson and Hinckley 1977). Three-dimensional models provide a complete conceptual p ic ture of gwv or Pn behavior for 2 i n t e r a c t i n g environmental v a r i a b l e s . Models of these types could be used as submodels in a larger system such as watershed management or ecosystem s tudies . L imi ta t ions to response model l ing, as presented, need to be recognized. Phenomenological models do not contain a time v a r i a b l e , as much as th i s i s an advantage, the model may break down without i t being used as an input parameter 122 (Thompson and Hinckley 1977). For example, phenomenological models do not describe hysteres i s which can occur during the day, nor consider endogenous rhythms which may a f fec t gwv or Pn. Integrated steady state models can not c o r r e c t l y describe the e f fects of qu ick ly changing dynamic condi t ions , such as sun f lecks under a forest canopy, or midday "sun shower". Photosynthetic rate dynamics i n response to l i g h t occurs i n a matter of seconds (Sal i sbury and Ross 1985). However, for stomata response to changing VPD, Watts and Nei l son (1978), studying Picea s i t c h e n s i s , reported that gwv changes began after 4-5 minutes, and a new steady state value was reached i n about 30-40 minutes. Johnson and F e r r e l l (1983), studying Picea engelmannii and Pseudotsuga  menzies i i found stomata responded qu ick ly to changes i n VPD, with the average response time being 30 seconds at high VPD, and 2 minutes at low VPD. The authors c r e d i t discrepancies i n response time for the two studies to the time constant of instruments used. Major determinants of gwv and Pn are l i g h t and VPD, but under c e r t a i n condit ions s o i l temperature, freezing overnight temperatures, and s o i l moisture can have modifying or dominating e f f ec t s . These factors were not included in th i s study, but could be incorporated i n future model development by producing a d d i t i o n a l 3-D models ( i . e . Pn to PAR and VPD), but at s p e c i f i c secondary factor l eve l s ( i . e . - 0 . 5 , - 1 . 0 , -1 .5 MPa s o i l drought) . I f i t i s determined that 123 these models, which are e s s e n t i a l l y 4-D i n nature, are s i m i l a r i n shape but lower in magnitude, models could be lowered or ra i sed through the x-y plane by determining responses ( i . e . Pn) at only a few PAR x VPD combinations. M u l t i p l e 2-D models have been produced th i s way (Turner et a l . 1 9 8 5 ) , but mult ip le 3-D models of th i s nature have not been reported in the l i t e r a t u r e . Two-dimensional phenomenological models require many data points to ensure that the l i m i t of a p h y s i o l o g i c a l v a r i a b l e has been reached over most of the defined range. In 3-D model l ing, s u f f i c i e n t data must be c o l l e c t e d for a l l combinations of the 2 environmental v a r i a b l e s . As much as the l i n e a r r e l a t i o n s h i p between PAR and VPD was overcome by using shade c l o t h , i t was d i f f i c u l t to record condit ions at low PAR and high VPD or high PAR and low VPD. Thus, Pn and gwv responses in these corners might be speculat ive in t erpre ta t ions of what the model p r e d i c t s . A model should be tested for v a l i d i t y , using actual data which had not been included in the o r i g i n a l development (Thompson and Hinckley 1 9 7 7 ) . Test ing was not done for the models developed. However, i t could be argued that , af ter a model was developed for a p a r t i c u l a r species / fo l iage type / p h y s i o l o g i c a l response for one treatment, i t was tested at l eas t 3 times using data from the three remaining treatments. A d d i t i o n a l l y , the i d e n t i c a l models (same components) were used for both f i r s t year and second year fo l iage for western hemlock. The exception was gwv to PAR 124 and VPD response model, because a wider VPD range was measured for second year f o l i a g e . Although the tests were not independent assessment for each stocktypes, they do v a l i d a t e model components used. Establishment of strong re la t ionsh ips between Pn or gwv and mult ip le environmental factors was made d i f f i c u l t by the interdependence of a l l var iab le s invo lved . No s ingle model can account for a l l poss ible events, or else i t becomes too complex and bulky to manage. Despite these l i m i t a t i o n s , simple models are necessary to understand seedl ing p h y s i o l o g i c a l response to d r i v i n g environmental parameters (Kuppers and Schulze 1985). Phenomenological models can be important for comparing species / stocktype s e n s i t i v i t i e s to p o t e n t i a l environmental condi t ions . Research into integrated steady-state measurements of p h y s i o l o g i c a l response ( i . e . gwv and Pn) over a wide range of environmental condit ions together with environmental condi t ion q u a n t i f i c a t i o n of p o t e n t i a l s i t e types might poss ib ly improve forest regeneration success. A p p l i c a t i o n s of Phenomenological Models The proper d e f i n i t i o n of seedl ing q u a l i t y i s "fitness for purpose" (Sutton 1988). This d e f i n i t i o n implies that we must not only quantify the seedl ing stocktypes' p h y s i o l o g i c a l c h a r a c t e r i s t i c s , but also must know beforehand i n some d e t a i l the environmental condit ions of the s i t e to be p lanted . The idea of knowing the p h y s i o l o g i c a l 125 c h a r a c t e r i s t i c s does not require stocktypes from each year from each nursery to be in t ens ive ly tested, but that a one time intens ive assessment of stocktypes be made and catalogued. Se lec t ion of stocktype for s p e c i f i c s i t e s would then be based on the one time intens ive assessment. An annual "mini" test could be performed to ensure stocktypes are developing to standards set by the intens ive t e s t . Phenomenological models of Pn and gwv were es tabl i shed using steady-state responses of gas exchange to a range of PAR and VPD. Hence, i t predicted carbon a s s i m i l a t i o n and water loss from known environmental inputs . Phenomenological models allow conceptual comparisons of species , genotype, or greenhouse c u l t u r a l treatment for p o t e n t i a l re fores ta t ion s i t e s . Af ter using phenomenological models, i t could be speculated that the order of greatest to l eas t response d i f ferences which could be detected are: species , stocktype, and genotype. These d i v i s i o n s w i l l each be discussed b r i e f l y . Tree species have inherent genetic d i f ferences which are sui ted to s p e c i f i c s i t e s . Species found on a s i t e p r i o r to harvest ing do not neces sar i ly ind icate which species i s best for growth and s u r v i v a l on the re fores ta t ion s i t e . A c loser examination of species p h y s i o l o g i c a l response c h a r a c t e r i s t i c s w i l l a l e r t foresters to the s h o r t f a l l s or advantages of species on c e r t a i n p lant ing s i t e s . Phenomenological models can point to species overlaps , so 126 that mult ip le species could be planted with a better degree of confidence. It would appear that species p h y s i o l o g i c a l response can be modif ied, depending on greenhouse c u l t u r a l regime. A l l stocktypes tested i n th i s study were of good q u a l i t y (Grossnickle et a l . 1990a). However, i t would appear that c e r t a i n stocktypes were better sui ted for cer ta in environments. More work i s necessary to determine the greenhouse c u l t u r a l treatment e f fect on p h y s i o l o g i c a l response of other tree species and genotypes. Leaf gas exchange processes have been used to assess poplar clones (Ceulemans and Impens 1980). For c o n i f e r s , gas exchange studies have been used to assess genetic f a m i l i e s , e .g . Pinus banksiana (Blake and Yeatman 1989), and Pinus  teada (Se i l er and Johnson 1988). Using the tools of biotechnology the advent of v iab le embryogenesis (cloning) i s current ly ava i lab le for a coni fer species , e . g . , Picea  glauca (Roberts et a l . 1990). It i s poss ib le that genetic combinations which prove to be superior af ter t e s t i n g , can be cyropreserved i n a deep freeze to form a l i b r a r y of genotypes (Sutton, Ben, Pers . Comm.). Along with genome storage, a p h y s i o l o g i c a l "f ingerprint" of genotype response can be stored on a computer d i sk . C e l l t i ssue of a desired genotype could be pul l ed out in the future , when the need for a s p e c i f i c p h y s i o l o g i c a l response a r i s e s . In order to complete the idea of f i tness for purpose, i t i s necessary to have c l i m a t i c information for the s i t e , 127 or a s i t e s imi lar to the one to be planted ( i . e . "site type"). C l imat i c data should be catalogued for hourly averages of day l ight PAR and VPD on amonthly bas i s . A ten by ten PAR x VPD defined matrix ranging from 0 to f u l l sun l ight , and 0 to the highest seasonal VPD would need to be created. Hourly environmental combinations would be categorized (average VPD and PAR l e v e l determined for each hour of the day each month) and then added together. Hourly environmental condit ions could be presented as 3-D response surface f igures ( i . e . z -axis = accumulated hours, y -ax i s = PAR, x-axis = VPD) summarizing the main atmospheric v a r i a b l e s for a s i t e type. When compared with p o t e n t i a l seedl ing p h y s i o l o g i c a l response i t forms a r i sk assessment methodology. These response graphs could qu ick ly indicate re fores ta t ion s i t e environmental l i m i t a t i o n s and/or point to the need for s p e c i f i c species , genotype and/or stocktype. In review, the necessary ingredients for using a seedl ing f i tness for purpose se l ec t ion program would be as fo l lows . F i r s t , se lect s i t e s which are designated for intens ive forest management such as those near m i l l s , pr ivate property , and/or s i t e s of good q u a l i t y . Second, develop a catalogue of species , genotype and stocktype p h y s i o l o g i c a l response, and accompanying morphological makeup. T h i r d , c o l l e c t s p e c i f i c re fores ta t ion s i t e environmental parameters, in p a r t i c u l a r accumulated hourly PAR and VPD for each s i t e type and noted monthly l i m i t a t i o n s to growth ( i . e . temperature, drought) . Fourth, develop an 128 a b i l i t y to produce (or clone) s p e c i e s , genotype, and/or stocktype combination e c o n o m i c a l l y . The i m p l i c a t i o n s are t h a t f o r e s t e r s c o u l d s e l e c t i n advance the proper combinations of s e e d l i n g i n p u t s ( s p e c i e s , genotype, and greenhouse c u l t u r a l stocktype) to best f i t p r o s p e c t i v e r e f o r e s t a t i o n s i t e s . 129 SUMMARY AND CONCLUSIONS The f indings show that daylength and moisture stress nursery c u l t u r a l treatments, as appl ied in th i s study, inf luenced p h y s i o l o g i c a l and morphological c h a r a c t e r i s t i c s of western hemlock and western red cedar. In th i s research study, ecophys io log ica l response of 4 DIT were monitored and re la ted to PAR and VPD on a high ava i lab l e s o i l moisture s i t e . The major f indings for western hemlock are as fol lows: F i r s t Year Needles 1) Short-day DIT had a higher gwv response to both increas ing VPD and PAR. 2) Both short-day and moisture s tress treatments improved Pn response to PAR, and the combination, SDD, had the highest response to increas ing PAR. 3) SDD DIT had the greatest Pn in response to VPD. 4) The above 2-D responses were re f l ec ted i n the gwv and Pn 3-D response surface with short-day DIT having higher gwv and Pn. 5) Short-day DIT seedlings were smal ler , shorter , had a better seedl ing water balance r a t i o and lower shoot to root r a t i o p r i o r to f i e l d p l a n t i n g . 130 Second Year Needles 1) Short-day DIT had a s l i g h t l y higher gwv response to both increas ing VPD and PAR. 2) No treatment di f ferences were found for Pn versus PAR. 3) The 3-D response surfaces showed both VPD and PAR were primary determinants of gwv and Pn. Stomata exhibi ted c losure at VPD greater than 3.5 KPa. 4) At the end of the growing season, LDD, SDD, and SDW DIT seedlings had higher shoot dry weight RGR. A l l stocktypes had s i m i l a r f i n a l morphological parameter values . The conclusion drawn i s that greenhouse c u l t u r a l treatments can inf luence p h y s i o l o g i c a l response of western hemlock f i r s t year needles. On f i r s t year needles, short-day DIT appears to p r i m a r i l y influence gwv, while moisture s tress DIT influences Pn. Growing i n high ava i lab le s o i l moisture condi t ions , short-day DIT continued to influence gwv of second year f o l i a g e . There was no continued influence of moisture s tress DIT on Pn of second year f o l i a g e . The major f indings for western red cedar are as fo l lows: F i r s t Year fo l iage 1) Moisture s tress DIT seedlings had greater Pn response to increas ing PAR and VPD. 2) Moisture stress DIT seedlings maintained a higher gwv response to changing PAR and VPD as compared to i t s non moisture s tress daylength counterparts . 131 3) The above 2-D responses were re f l ec ted i n gwv and Pn 3-D response surfaces with moisture stressed DIT having higher gwv and Pn. 4) LDW DIT seedlings had the larges t shoot and root systems p r i o r to f i e l d p l a n t i n g . Second Year fo l iage 1) Second year fo l iage exhibi ted no treatment d i f ference for gwv and Pn response to PAR and VPD. 2) Pn response to increas ing PAR showed no i rradiance saturat ion l e v e l . 3) The 3-D response surfaces of gwv and Pn showed that both VPD and PAR are primary determinants of gwv and Pn. Stomata exhibi ted no signs of c lo s ing up to VPD l eve l s of 4.0 kPa. 4) A l l stocktypes had s imi lar f i n a l morphology parameter values . In conc lus ion , western red cedar greenhouse c u l t u r a l treatments can inf luence p h y s i o l o g i c a l response. Moisture s tress appears to be the most i n f l u e n t i a l DIT exh ib i t ing moderate e f fects on Pn and gwv. Stocktype treatments showed no inf luence on second year fo l iage Pn and gwv response to PAR or VPD. Three p h y s i o l o g i c a l response assessments were used to character ize stocktypes. Attempts to test stocktype response at stable environmental condit ions proved at times d i f f i c u l t to contro l i n the f i e l d , and p o t e n t i a l l y can produce large 132 measurement v a r i a t i o n which may not be a t t r i b u t e d to stocktype e f f e c t . Boundary l i n e a n a l y s i s , i f used c o r r e c t l y and with s u f f i c i e n t data, o f fers a good stocktype assessment method which enables the i s o l a t i o n of a phys io log i ca l response to one environmental v a r i a b l e . Three dimensional surface response technique i s required to provide a c learer conceptual representat ion of 2 primary environmental var iab le s influence on a seedlings p h y s i o l o g i c a l response. The se l ec t ion for a best performing species / genotype / c u l t u r a l treatment for a s p e c i f i c f i e l d s i t e type must be based on foreknowledge of po ten t ia l stocktype response and l i m i t i n g environmental condit ions of the re fores ta t ion s i t e . Boundary l i n e and 3-D response surface analys i s contribute to understanding p o t e n t i a l p h y s i o l o g i c a l response to environmental condi t ions . 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LANGLEY, B.C., V3A SES ' GROWER B.C. RESEARCH 3650 WESBROQK MALL VANCOUVER, B.C. V6S 2L2 A t t e n t i o n o-f: JOHN MAJORS LEGAL LOCATION Sample d e s c r i p t i o n : SOIL SAMPLE W.O. NUMBER PAGE LAB NUMBER SAMPLE RECEIVED: [ 0 3 - 2 1 J - 1 9 8 8 ANALYSIS COMPLETED: 0 4 ^ 2 1 - 1 9 8 8 SAMPLE RETAINED UNTIL: f " " o r 6 0 d a y s FOR INFORMATION C A L L D r . T . G u t h r i e SAMPLE NUTRIENT ANALYSIS (P.P.M.) DEPTH AMMONIUM NITRATE PHOSPHATE POTASSIUM SULPHATE CALCIUM SODIUM MAGNESIUM IRON COPPER ZINC BORON MANGANESE UCAV10OIUM •...'..IS,. 5 9 2 0 8 1 4 2 0 . 5 1 1 6 0 7 8 6 8 0 . 8 3 . 9 0 . 6 6 TOTAL L B S J A C R E 7 1 2 3 0 4 2 0 8 0 . 7 1 6 9 6 1 1 4 9 9 1 . 2 5 . 7 0 . 9 . 9 ' . i i-M; EXCESS * '• ### OPTIMUM ### ### ### ### am ### MARGINAL ### mm tfitif ### ### mtu ### ### ### • ### ##U ### ### ### ### mt# mm ### ### DEFICIENT ### ### ### t;m mm ### ### ### ##•# ### ### #m • •••••• -.aWM- \J_\ Ca m Mg Fe Cu B " ' SAMPLE DEPTH , PH (ACIDC SOIL QUALITY EC. (SALINITY) ORGANIC MATTER TEXTURE Min For Droning trees I shrubs apply NIIROBEN at a rate of 1.5 lb per 1000 sq.ft. prior to planting or at 1.0 lb/1000 sq.ft. i n early spring tc established plants. Additional N tan be added up to 1.5 lb/1000 sq.ft. Hith last application before Sep tetter, No PHOSPHORUS application required. SOIL: RECOMMENDATIONS CROPPING PRACTICE: • • • ^^^fmm^m LIME AND MICRONUTRIENTS Add POTASSIUK at a rate of 0.5 lb K20/1000 sq.ft. Dc not exceed 2 lb per application. Add 50 lb/1000 sq.ft. of LIKE (not evergreens). Hg Ion. Add nagnesiun at 1.0 lb-figO per 100C sq.ft. Sulphur lo*. Add sulphur at 0.5 lb-S per lOOOsq.ft. At lesst one •icrjnstrient is rated as IOM. $>ply Boron us ing Borax at ra te of 1/4 3/1000 s q . f t . C R O P ENVIRONMENT CONDITION CROP CHOICE EXCELLENT AVERAGE Trees and scrubs -*ST. EXPECTED £ B L D S P*05 P L A C E D CX BROADCAST K,0 A ten of isn-in (ijjut 1.5 cu.vj,: ml! supply iparc»ipjtely Z Ifc-H, 2 1&-P205 5 lo-K20 per 1.000 sq.ft. Soluble salts cay be Mod. CaiiYSrsJcr.s: ; ficre= <3,0M feet = 0.40 KKtjrss 1 cubic yard = 0.8 cubic deters 1 lb/acre= 1.12 kg/ha 155 Appendix IB. S o i l nutrient analys is report of U . B . C . f i e l d s i t e for J u l y , 1988. Analys is was prepared by Norwest S o i l Research I n c . , 203 - 20771 Langley Bypass, Langley, B . C . , V3A 5E8. 156 N O R W E S T L A B S 4526 8 8 3 6 3 9 l lORWEST S O I L R E S E A R C H I M C . 2 0 3 2 0 7 7 1 L A N G L E Y B Y P A S S , L A N G L E Y , B . C . , V 3 A 5 E B GROWER B . C . R E S E A R C H 3 6 5 0 W E S B R O O K M A L L V A N C O U V E R , B . C . V 6 S 21 .2 A t t e n t i o n o - f : J O H N MAJOR-LEGAL LOCATION S a m p l e d e s c r i p t i o n : S O I L W.O. NUMBER PAGE LAB NUMBER SAMPLE RECEIVED: C2Zz2^T 9 8 8 ANALYSIS COMPLETED: 0 8 ~ 0 o - 1 9 8 8 SAMPLE RETAINED UNTIL: F o r 6 C l d a y s FOR INFORMATION CALLJDr . T . G u t h r i e SAMPLE DEPTH . NUTRIENT ANALYSIS (P.P.M.) DEFICIENT ..:.V'.,-', :t, : SAMPLE" >.98 0 . 1 9 6.7 M i n For growing trees I shrubs apply NITROGEN at a rate of 1.5 lb per 1000 sq.ft. prior to planting or at 1.0 lb/1000 sq.ft. in early spring to established plants. Additional N can be added up to l.S lb/1000 sq.ft. Kith last application before September. No PHOSPHORUS application required. RECOMMENDATIONS CROPPING PRACTICE: —-—• ^-^mmm LIME AND MICRONUTRIENTS ^-"VA ' CROP ENVIRONMENT CONDITION CROP CHOICE EXCELLENT Trees ar.d «lrubs POOR ICTED LDS PA PLACED oienOACCAST K,0 Add POTASSIUM at a rate of 2 lb K20/1000 sq.ft. Do not exceed 2 lb per application. Add 50 lb/1000 sq.ft. of LINE (not evergreens). Hg ION. Add aagnesiua at 1.0 lb-KgO per 1000 sq.ft. Sulphur low. Add sulphur at 0.5 lb-S per lOOOsq.ft. At least one licronutrient is rated as low. Apply Boron us ing Borax at ra te of 4 OZ . / 1 0 0 0 s q . f t . A ton of aahure (about 1.5 cu.yd.) M i l l supply approximately 3 lb-N, 2 lb-P205 i 5 Ib-K20 per 1,000 sq.ft. Soluble salts lay be high. Conversions: I Acre= 43,000 square fee! - 0.40 Hectares 1 cubic yard = 0.8 cubic deters 1 lb/acre= 1.12 kg/ha 157 APPENDIX 2 Experimental Design of Field Layout WESTERN HEMLOCK WESTERN RED CEDAR BLOCK 1 ( 1 ) LDD<2> . . . 20 LDW . . . . . . 20 . . . 20 . . . 20 . . . 20 . . . 20 LDW . . . 20 . . . 20 SDD . . . 20 . . . 20 SDD . . . 20 . . . 20 LDD . . . 20 SDW . . . . . . 20 LDW . . . 20 SDD . . . . . . 20 . . . 20 SDD . . . . . . 20 LDD . . . 20 . . . 20 SDD . . 20 . . 20 . . 20 . . 20 SDW . . 20 . . 20 LDW . . 20 . . 20 . . 20 SDW . . 20 . . 20 SDD . . 20 . . 20 SDD . . 20 . . 20 LDW . . 20 LDD . . . . . 20 . . 20 SDW . . . , . 20 BLOCK 2 SDW . . 20 LDD . . . . . 20 LDD . . 20 . . 20 SDD . . 20 LDD . . . . . 20 LDD . . 20 . . 20 SDD . . 20 . . 20 . , 20 SDW '. . . . . 20 . . 20 . . 20 . . 20 . . 20 . . 20 SDW . . . . . 20 LDW . . 20 SDD . . . . . 20 . . 20 LDW . . . . . 20 SDD . . 20 LDD . . . . . 20 SDW . . 20 LDD . . . . . 20 LDD . . 20 SDW . . . . , 20 . . 20 SDD . . . . . 20 SDW . . 20 SDW . . . . . 20 SDD . . 20 . . 20 LDD . , 20 LDD . . . . . 20 . , 20 LDW . . . . , 20 SDW 20 SDD . . . . , 20 ( 1 ) There are five (5) rows of each treatment in each block. There are twenty (20 ) r eplicates in each row. For morphological evaluation, one tree was randomly selected from each row. LDD = Long-day dry LDW = Long-day wet SDD = Short-day dry SDW = Short-day wet 158 Appendix 3. S o i l water retention curve of U . B . C . f i e l d s i t e . Three in tac t core samples were used. Ana lys i s and curve by Soi lcon Laborator ies , 105 - 2931 Olafson Ave . , Richmond, B . C . , V6X 2R4. 

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