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Resistance to water uptake by conifer seedlings Dosskey, Michael Gordon 1978

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RESISTANCE TO WATER UPTAKE BY CONIFER SEEDLINGS by Michael Gordon Dosskey B.Sc, Oregon State University, 1974 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES (Faculty of Forestry, Forest S o i l s ) We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA September, 1978 0 Michael Gordon Dosskey, 1978 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of Brit ish 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 representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department pf The University of Brit ish Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date £>c~f. 6 . /97<£ / i i ABSTRACT Water a v a i l a b i l i t y for uptake by tree seedlings i s determined both by the s o i l water potential i n r e l a t i o n to seedling needle water potential and by the resistance to flow of water through the s o i l , root and stem, to the needles. This study was designed to focus p r i n c i p a l l y on water uptake resistances. The effects of s o i l texture and tree species on this water uptake resistance were quantified through the use of an Ohm's Law model suited to water flow through the soi l - p l a n t system. The study was conducted on one-year-old potted seedlings i n a controlled environment growth chamber. Needle water potential (^) of Douglas-fir i s not much affected by s o i l water potential ( ' r ' g ) down to about - 2 . 5 MPa, where the calculated water uptake rate becomes very small. However, s o i l texture does s i g n i f i c a n t l y affect the resistance to flow into the seedling and thus affects the water uptake rate by the seedling. The t o t a l resistance to water uptake increases as the s o i l dries. Coarser textured s o i l s show consistently higher water uptake resistances over the s o i l water potential range - 0 . 5 to - 2 . 5 MPa. It i s inferred that differences i n resistance are associated with unsaturated, hydraulic conductivity characteristics of the s o i l and so i l - r o o t contact. Unlike Douglas-fir, both western and mountain hemlock show a large decrease i n needle water potential as the s o i l dries down to / i i i a of about -3.0 MPa. The water potential difference (ip - ) for hemlocks i s less where i s higher than -1.8 MPa, and greater where i|> i s less than -1.8 MPa, than (<p - ) for Douglas-fir i n these s s N experiments. Despite these differences, the resistance to water uptake for both hemlock species i s much greater over the s o i l water potential range -0.5 to -2.5 MPa, and thus the water uptake rates are much less than for Douglas-fir with the same s o i l , even though root densities and root surface areas are much larger for the hemlocks. This behavior i s most pronounced with mountain hemlock. These differences are thought to be related to higher tissue and (perhaps) s o i l - r o o t contact resistances i n the hemlock species. The s o i l resistance appears to be small, at least down to ip of about -2.0 MPa, i n these experiments. However, root densities are probably much greater than one might expect i n the f i e l d . TABLE OF CONTENTS Page ABSTRACT i i TABLE OF CONTENTS i v LIST OF FIGURES v i . ACKNOWLEDGEMENTS x CHAPTER 1: INTRODUCTION 1 CHAPTER 2: LITERATURE REVIEW AND THEORY 3 CHAPTER 3: METHODS AND MATERIALS 10 3.1 Experimental Treatments 10 3.2 Strategy 11 3.3 Experimental Preparations 12 3.3.1 Seedling Preparation 12 3.3.2 Experimental Environment 17 3.4 Experimental and An a l y t i c a l Procedures 18 3.4.1 Water Potential 18 3.4.2 Water Uptake Rate 24 3.4.3 Resistance 32 CHAPTER 4: RESULTS AND DISCUSSION: SOILS 33 4.1 Water Potential 33 4.2 Water Uptake Rate 33 4.3 Resistance 35 4.4 Discussion 36 CHAPTER 5: RESULTS AND DISCUSSION: SPECIES 50 5.1 Water Potential 50 5.2 Water Uptake Rate 50 Page 5.3 Resistance 52 5.4 Discussion 53 CHAPTER 6: SUMMARY AND CONCLUSIONS 68 REFERENCES 70 APPENDICES 75 / v i LIST OF FIGURES Number Page l a Needle water potential i n r e l a t i o n to s o i l water potential for Douglas-fir on s i l t y clay s o i l . . . . 39 lb Needle water potential i n r e l a t i o n to s o i l water potential for Douglas-fir on s i l t loam s o i l . . . . 40 l c Needle water potential i n r e l a t i o n to s o i l water potential for Douglas-fir on loamy sand s o i l . . . . 41 2 Needle water potential i n re l a t i o n to s o i l water potential for Douglas-fir: A comparison of s o i l s ; s i l t y clay (SiC), s i l t loam (SiL) and loamy sand (LS) 42 3 Water potential difference i n r e l a t i o n to s o i l water potential for Douglas-fir: A comparison of s o i l s ; s i l t y clay (SiC), s i l t loam (SiL) and loamy sand (LS) 43 4a Average seedling water uptake rate per unit root surface area i n r e l a t i o n to s o i l water potential for Douglas-fir on s i l t y clay s o i l 44 4b Average seedling water uptake rate per unit root surface area i n r e l a t i o n to s o i l water potential for Douglas-fir on s i l t loam s o i l 45 4c Average seedling water uptake rate per unit root surface area i n re l a t i o n to s o i l water potential for Douglas-fir on loamy sand s o i l 46 / v i i Number Page 5 Average seedling water uptake rate per unit root surface area i n r e l a t i o n to s o i l water potential for Douglas-fir: A comparison of s o i l s ; s i l t y clay (SiC) , s i l t loam (SiL) and loamy sand (LS) 47 6 Average seedling water uptake rate i n r e l a t i o n to s o i l water potential for Douglas-fir: A comparison of s o i l s ; s i l t y clay (SiC), s i l t loam (SiL) and loamy sand (LS) 48 7 Average seedling water uptake resistance i n r e l a t i o n to s o i l water potential for Douglas-fir: A comparison of s o i l s ; s i l t y clay (SiC), s i l t loam (SiL) and loamy sand (LS) 49 8a Needle water potential i n r e l a t i o n to s o i l water potential for Douglas-fir on s i l t loam s o i l . . . . 56 8b Needle water potential i n r e l a t i o n to s o i l water potential for western hemlock on s i l t loam s o i l . . 57 8c Needle water potential i n r e l a t i o n to s o i l water potential for mountain hemlock on s i l t loam s o i l . . 58 9 Needle water potential i n r e l a t i o n to s o i l water potential for seedlings on s i l t loam s o i l : A comparison of species; Douglas-fir (DF), western hemlock (WH) and mountain hemlock (MH) . 59 / v i i i Number Page 10 Water potential difference i n r e l a t i o n to s o i l water potential for seedlings on s i l t loam s o i l : A comparison of species; Douglas-fir (DF), western hemlock (WH) and mountain hemlock (MH) 60 11a Average seedling water uptake rate per unit root surface area i n r e l a t i o n to s o i l water potential for Douglas-fir on s i l t loam clay 61 l i b Average seedling water uptake rate per unit root surface area i n r e l a t i o n to s o i l water potential for western hemlock on s i l t loam s o i l 62 11c Average seedling water uptake rate per unit root surface area i n r e l a t i o n to s o i l water potential for mountain hemlock on s i l t loam s o i l 63 12 Average seedling water uptake rate per unit root surface area i n r e l a t i o n to s o i l water potential for seedlings on s i l t loam s o i l : A comparison of species; Douglas-fir (DF), western hemlock (WH) and mountain hemlock (MH) 64 13 Average seedling water uptake rate i n r e l a t i o n to s o i l water potential for seedlings on s i l t loam s o i l : A comparison of species; Douglas-fir (DF), western hemlock (WH) and mountain hemlock (MH) . . . 65 Average seedling water uptake resistance i n r e l a t i o n to s o i l water potential for seedlings on s i l t loam s o i l : A comparison of species; Douglas-fir (DF), western hemlock (WH) and mountain hemlock (MH) Average seedling water uptake resistance on a unit root surface area basis i n r e l a t i o n to s o i l water potential for seedlings on s i l t loam s o i l : A comparison of species; Douglas-fir (DF), western hemlock (WH) and mountain hemlock (MH) ACKNOWLEDGEMENTS I wish to express my sincere gratitude and appreciation to Dr. T. M. Ballard (Associate Professor, Dept. of S o i l Science and Faculty of Forestry) for his supervision and guidance of my whole M. Sc. program, and for his valuable encouragement, c r i t i c i s m s , editing advice and patience through the production of this thesis. I also wish to thank Dr. T. A. Black (Associate Professor, Dept. of S o i l Science) for invaluable discussions of theory and technical advice throughout t h i s study. My appreciation also goes to the other members of my committee: Dr. P. G. Haddock (Professor, Faculty of Forestry) and Dr. J. P. Kimmins (Associate Professor, Faculty of Forestry) for their c r i t i c a l review of each thesis draft. I extend my thanks to the Faculty of Forestry for their acceptance of me into the M.Sc. program at U.B.C, to the Department of S o i l Science for use of laboratory f a c i l i t i e s , and to Mrs. J. Hollands for her excellent typescript of this thesis. F i n a l l y , my wholehearted and sincere thanks go to my family and friends for their encouragement, companionship and precious friendship. This study was funded i n part by a grant from the U.B.C. Research Committee. II CHAPTER 1: INTRODUCTION Unlike factors affecting water loss from leaves, some factors affecting water uptake by plants are not well understood, especially with regard to tree species. Water stress i n tree seedlings, which results from an imbalance between loss and uptake, i s recognized as a major contributor to forest regeneration f a i l u r e s i n western North America, where the growing season coincides with hot, dry summers (Isaac, 1935; Kummel, et al., 1944; Utzig and Herring, 1974). In western Oregon and Washington and southern coastal B r i t i s h Columbia, Douglas-fir (Pseudotsuga menziesi.i var. menziesii (Mirb.) Franco) i s by far the most widely used reforestation species. However, western hemlock (Tsuga heterophylla (Raf.) Sarg.) i s being used increasingly i n wetter areas, and mountain hemlock (Tsuga mertensiana (Bong.) Carr.) at higher elevations (Waring, 1970; Van Eerden, 1974; Dimock et al., 1976; Stein, 1976). Considerable information exists on the water relations of Douglas-fir under low water stress conditions, but l i t t l e i s available concerning i t s behavior under high stress conditions. In addition, very l i t t l e information at a l l i s available concerning water stress relationships of either hemlock species. Clearly, knowledge of water uptake characteristics of these species over a wide range of moisture conditions would be very useful for describing water stress relationships 12 i n order to f a c i l i t a t e assessment and prevention of regeneration f a i l u r e s with these species. A characteristic of the mountainous te r r a i n of this region i s the wide variety of surface s o i l materials i n which seedlings must extract water i f they are to survive and grow. The water flow properties of these materials might be very important to water uptake by seedlings. The objective of this study was to quantify water uptake by these three species and to assess some factors influencing t h i s uptake from different s o i l materials. /3 CHAPTER 2: LITERATURE REVIEW AND THEORY Often the only s o i l factor evaluated i n r e l a t i o n to water stress i s the s o i l water p o t e n t i a l , a measure of the energy required to remove water from the s o i l . However, the resistance to water flow between s o i l and plant may also be si g n i f i c a n t (Gardner, 1960; Cowan, 1965). This resistance might vary from s o i l to s o i l , at the same water potential, because of hydraulic conductivity differences. Even i n the same s o i l , the resistance might vary from seedling to seedling because of differences i n root d i s t r i b u t i o n or tissue conductivity. This study was designed to focus p r i n c i p a l l y on t h i s matter of water flow resistances. Water taken up by the seedling flows through the s o i l to the root surfaces whence i t passes r a d i a l l y across the root to the xylem, i n which i t moves upward toward the transpiring leaf surfaces. Water moves i n response to water potential energy differences, from regions of high water potential energy, e.g. i n the s o i l , toward regions of lower water potential energy, e.g. i n the leaves. The rate of flow through a l l or any portion of the pathway i s proportional to the magnitude of the water potential difference across that portion of the pathway and inversely proportional to the resistance to water flow along that pathway. Symbolically stated, /4 where U i s the water uptake rate, ip and are the water potentials at either end of the pathway, and R i s the resistance to water flow. This equation i s analogous to Ohm's Law describing e l e c t r i c a l current flow and can be used as a simple model to describe water flow through the s o i l - p l a n t system (van den Honert, 1948; Cowan, 1965; H i l l e l , 1971). At steady state, where the uptake rate i s the same through a l l parts of the system, the t o t a l resistance (R) can be described by the sum of a l l series-linked resistances i n the pathway. Any change in resistance i n one segment w i l l change the t o t a l resistance and hence change the flow rate and/or the water potentials as the system moves toward a new steady state condition. Thus, the t o t a l water uptake system can be considered as a continuum of dynamically interdependent segments ( P h i l i p , 1966). Water uptake by the plant appears to be i n passive response to water potential differences except, perhaps, at very low water uptake rates, where active uptake, i f i t does occur, may become r e l a t i v e l y large (Kramer, 1969; Cowan, 1965). Over most of the water uptake range, the water uptake resistance (R) through any segment of the pathway i s dependent upon the path length of that segment, the cross-sectional area of that flow pathway, and the hydraulic conductivities of the pathway media. In the s o i l , water moves dominantly i n the l i q u i d phase, but vapor di f f u s i o n becomes increasingly important as the s o i l becomes drier ( P h i l i p , 1966). In the plant, flow i s i n the l i q u i d phase by 15 d i f f u s i o n across membranes or as viscous flow through conducting tissues. Thus, there are several different mechanisms of water transport through the s o i l - p l a n t system, and the contributions of these mechanisms vary i n magnitude. Accordingly, resistance may vary with environmental conditions and the t o t a l resistance of the pathway might be dominated by different component resistances under different conditions. Rearranging equation (1) to get *1 " h R = — — ( 2 ) allows us to quantitatively evaluate the t o t a l resistance to water uptake by equating ^ and ip to s o i l and needle water p o t e n t i a l , respectively, and U to the water uptake rate. Recent studies have shown that for some plants rooted i n s o i l , the t o t a l resistance to water uptake from the s o i l to leaves increases as the s o i l dries (Taylor and Klepper, 1975; among others). Thus, the decrease i n water uptake rate that i s normally observed as the s o i l dries i s greater than can be simply explained by a change i n the water potentials i n s o i l and leaves. However, there i s considerable debate over which segments of the pathway offer the greatest resistance and under what conditions they might do so. Studies on a few herbaceous and woody species, with roots i n solution, indicate the presence of a very large resistance to water flow i n the roots (Jensen 6t at. , 1961; T i n k l i n and Weatherley, 1966; /6 Boyer, 1969; Stoker and Weatherley, 1971). In many plants, most of t h i s resistance probably occurs r a d i a l l y across the root to the xylem (Lang and Gardner, 1970; Boyer, 1971). In a variety of plants, resistance to flow through the stem appears to be r e l a t i v e l y small (Jensen et al., 1961; T i n k l i n and Weatherley, 1966; Boyer, 1971; Herkelrath et al., 1977a). Indications are that resistances through roots and through the stem vary and increase as the flow rate decreases (Tinklin and Weatherley, 1966; Kozlowski, 1966; Andrews and Newman, 1969), although the mechanism i s uncertain. For plants rooted i n s o i l , the resistance to water flow through the s o i l to the root may be s i g n i f i c a n t . Gardner (1960) pointed out that water flows less easily through s o i l as the s o i l d ries, since the unsaturated hydraulic conductivity decreases rapidly as the water content, and, hence, the s o i l water potential decreases. His calculations indicate that the resistance through s o i l may become s i g n i f i c a n t l y large as the s o i l water potential f a l l s below -0.5 MPa, but that the magnitude of t h i s resistance i s highly dependent upon the amount of absorbing root surface area and i t s d i s t r i b u t i o n through the s o i l volume, as these affect both the absorbing pathway's cross-sectional area and the average distance water must flow through the s o i l to the roots (Gardner, 1960; 1964). It i s generally agreed that for plants rooted i n very wet s o i l , the resistance to water flow through the plant i s much larger than that through the s o i l , but that s o i l resistance becomes II increasingly important as the s o i l dries. However, there i s considerable debate about the condition under which s o i l resistance becomes s i g n i f i c a n t and dominant i n r e l a t i o n to the t o t a l resistance. Boyer (1969) reported plant resistance to be t h i r t y times as great as that i n moist s o i l for sunflower. Others have claimed that s o i l resistance remains smaller than plant resistance even down to -1.5 MPa and beyond (Andrews and Newman, 1969; Newman, 1969a). But T i n k l i n and Weatherley (1968) inferred, from thei r data, s i g n i f i c a n t resistance i n the s o i l adjacent to roots i n sand, even though the s o i l water potential of the bulk s o i l was only-0.0025 MPa. However, after reviewing the evidence, Newman (1969b) claimed that there i s s t i l l no d e f i n i t i v e evidence that the s o i l resistance i s l i m i t i n g at s o i l water potentials above -0.7 MPa, under normal rooting conditions. More recently, studies by Herkelrath et al. (1977a, 1977b) have indicated the presence of si g n i f i c a n t resistance i n the region of the roots which cannot be explained by the addition of s o i l and plant resistances alone. They suggest that this resistance i s located at the so i l - r o o t boundary, and increases as the s o i l dries, as a result of decreasing contact between water films around s o i l p a r t i c l e s and the root surface. This has the effect of decreasing the effective area of l i q u i d s o i l water contact with root surfaces. This resistance may be compounded by root shrinkage, which has been found to occur with increasing plant water stress (Huck et al., 1970). Nnyamah et al. (1978) found that s o i l - r o o t contact resistance could /8 account for as much as one-half of the t o t a l resistance between bulk s o i l and root xylem i n 20 year-old Douglas-fir trees. Resistance to water flow through the s o i l , to and into the root may be modified by mycorrhizal fungi. In very wet s o i l , S a f i r et al. (1971) found lower resistances to water uptake by endomycorrhizal soybean plants than those without mycorrhizae. They suggested several possible mechanisms for this observed behavior, including an increase i n the effective absorbing surface area provided by fungal hyphae, and perhaps, penetration of the root cortex by fungal hyphae providing a lower resistance pathway for water movement r a d i a l l y across the root to the xylem. In view of Herkelrath's s o i l - r o o t contact resistance hypothesis, the physical presence of a fungal mantle around absorbing roots might also provide an increasingly important bridge for l i q u i d flow across any developing vapor gap as the s o i l dries. Clearly, both s o i l and plant factors influence the resistance to water uptake, and these factors are variable, but their summed effect i s to increase the t o t a l resistance as the s o i l dries, at least for plants reported in the l i t e r a t u r e . Resistance i n the region of the roots appears to dominate, whether i t l i e s i n the s o i l , roots or both. The r e l a t i v e magnitudes of these component resistances vary with species and s o i l and plant conditions. Through equation (2), the t o t a l water uptake resistance can be quantified for tree species. Although the resistance for components of the pathway cannot be quantified without intermediate /9 water potential measurement between s o i l and needles, comparison of t o t a l resistances i n response to treatment can be informative. Evaluating the t o t a l resistance (R) for seedlings of the same species and similar s i z e , but rooted i n s o i l s of d i f f e r i n g 0 hydraulic conductivity ch a r a c t e r i s t i c s , w i l l allow us to quantify the effect of s o i l water conductivity on water uptake rates and water stress. Evaluation of t o t a l resistance for seedlings of different species rooted on the same s o i l w i l l allow comparison of the. combined effects of root d i s t r i b u t i o n and soi l - r o o t contact as well as tissue resistance differences. These comparisons can be made over a wide range of s o i l water potentials as the s o i l dries. n o CHAPTER 3: METHODS AND MATERIALS 3.1. Experimental Treatments Considerable physiological information i s available for Douglas-fir which can f a c i l i t a t e analysis of experimental data i n t h i s study. For t h i s reason, Douglas-fir seedlings from a medium-elevation (500 meters) provenance were chosen as the yardstick by which s o i l and species treatments can be compared. Western and mountain hemlock seedlings were obtained from coastal provenances of similar medium elevation (1100 meters). A l l seedlings were obtained from B r i t i s h Columbia Forest Service nurseries. (For provenance descriptions, see Appendix 2.) Since, i n theory, pore size d i s t r i b u t i o n and arrangement greatly influence the relationship between s o i l water potential and unsaturated hydraulic conductivity of the s o i l , and since they are known to be influenced by p a r t i c l e size d i s t r i b u t i o n , three s o i l s of widely d i f f e r i n g texture were chosen to test the effect of s o i l water flow characteristics on water uptake. The s o i l s , s i l t y clay, s i l t loam and loamy sand, were obtained from Ap horizons at the University of B r i t i s h Columbia Research Forest and represent the range of surface materials commonly found i n this region. These s o i l s were expected to y i e l d a wide range of unsaturated hydraulic conductivity ch a r a c t e r i s t i c s . (For s o i l properties, see Appendices 3, 4, and 5.) Ill 3.2 Strategy Ideally, concurrent knowledge of fluxes and water potential differences would require simultaneous measurement of these parameters on the same seedling. However, the lack of simple non-destructive plant water potential measurement techniques forced the study to be developed around separate studies of water uptake and water potential difference, on large sample populations under similar environmental conditions. Because of the complexity of the environmental variables concerned, experiments were conducted on one-year-old potted seedlings i n growth chambers. Under growth chamber conditions, s o i l water potential can be used as the independent variable to which uptake rate and water potential difference can be related. A l l measurements were treated as steady state values and were taken at times when this condition was closely approximated. The average needle water potential C ^ ) was measured using sample chambers with dew-point hygrometers on excised needles. Concurrently, dew-point hygrometer probes were used i n the s o i l to measure the s o i l water potential ( i j ^ ) , which was assumed to represent the average s o i l water potential at a point approximately halfway between roots. In calculating water potential difference - ip ) , the g r a v i tational potential difference was ignored, as i t i s of the order of only 10 kPa, a magnitude too small to have a si g n i f i c a n t effect i n interpreting the results. Evapotranspiration was evaluated i n terms of weight loss rate over four-hour periods when steady state was , approximated. Evaporation rate was estimated as the asymptotic value 112 of weight loss rate plotted over s o i l water potential since, under very dry s o i l conditions, the transpiration rate becomes very nearly zero, and since evaporation rate was r e s t r i c t e d to a near constant rate over the f u l l s o i l water potential range used i n these experiments. Constant evaporation rates were approximately achieved by enclosing the s o i l i n p l a s t i c bags which r e s t r i c t e d the vapor pressure gradient and the vapor di f f u s i o n resistance to nearly constant magnitudes. At approximately steady state, transpiration rate i s very nearly equal to water uptake rate and thus was used as a reasonable approximation of water uptake rate i n these experiments. Using equation 2 from the previous chapter, resistance to water uptake was calculated for each treatment over the range where s i g n i f i c a n t water uptake occurred, or approximately -0.5 to -2.5 MPa s o i l water potential. 3.3 Experimental Preparation 3.3.1 Seedling Preparation In order to be able to attribute experimental differences to experimental treatments, a l l samples were handled s i m i l a r l y before and during experimental periods. In order to reduce var i a t i o n within treatments, environmental extremes were avoided before experimentation and a l l seedlings were prepared i n a manner such that, within treatments, they would exhibit similar size and form without seriously a l t e r i n g the chara c t e r i s t i c behavior of the treatment. The preparations included (1) potting conditions /13 and techniques, (2) pruning, (3) greenhouse environment including watering and f e r t i l i z a t i o n schedules, and (4) selection and preparation for experimentation. Five hundred seedlings each, of six-month-old styroblock western and mountain hemlock, and one thousand six-month-old plug Douglas-fir were obtained from B r i t i s h Columbia Forest Service nursery cold storage warehouses i n Surrey and Duncan, respectively, i n March, 1976. The seedlings were stored i n a refr i g e r a t i o n unit on the U.B.C. campus for three weeks u n t i l potting. At that time, seedlings showing mold, breakage and obvious crown or root deficiencies or excesses were discarded. The three s o i l s were sieved while moist, through a 5-mm mesh. Since very l i t t l e gravel was present, further sieving was not considered necessary. A l l hemlock seedlings were potted i n the medium texture ( s i l t loam) s o i l and equal numbers of Douglas-fir were potted i n a l l three s o i l s i n early A p r i l , 1976. At the time of potting, the roots were gently washed to 3 remove the nursery s o i l mix, and transplanted into 150-cm (5.7-cm wide) p l a s t i c pots, using pre-weighed amounts of s o i l packed to equal volumes. This allowed close control and calculation of s o i l bulk density for a l l treatments. The bulk -3 density of the s i l t y clay was about 500 kg-m , s i l t loam -3 -3 750 kg*m and loamy sand 1120 kg*m /14 A l l seedlings flushed within three weeks after potting. Within one month, obvious va r i a t i o n i n crown size was observed. To reduce this v a r i a t i o n , the seedlings were l i g h t l y pruned to similar needle surface areas. Approximately 15% of each treatment population was discarded due to deficient or excessive crown sizes. It was hoped that pruning would also i n d i r e c t l y control root growth of larger seedlings. The attempt to equalize needle surface areas was hindered by the indeterminate behavior of the hemlocks. However, a second flush by the Douglas-fir i n early summer did reduce differences between species. The seedlings were kept i n the greenhouse u n t i l experimentation. The v e n t i l a t i o n system maintained daytime temperatures between 20 and 25°C, with a r e l a t i v e humidity of about 80%. Irradiance during the daytime was probably 20 zo 25% of f u l l sunlight. The seedlings were watered to f i e l d capacity daily on sunny days, .and every other day on cool or cloudy days. This frequency was necessary i n order to maintain s o i l water potentials above -0.5 MPa. I t was soon noticed that the hemlock pots dried much more slowly than those of Douglas-fir, so the frequency of watering of hemlock seedlings was reduced to avoid overwatering. It was hoped that pruning to similar crown sizes would help reduce this kind of variation within treatments. /15 A l l seedlings were f e r t i l i z e d regularly with 5.0 ml of f u l l strength modified Hoagland's solution (see Appendix 1) during the period of rapid growth i n spring, and then p e r i o d i c a l l y thereafter. F e r t i l i z a t i o n was intended to prevent deficiency symptoms which might affect water uptake behavior and normal growth, and possibly discourage i n f e c t i o n of root systems by mycorrhizal fungi which might complicate experimental res u l t s . The seedlings were kept i n the greenhouse from March u n t i l the end of experiments i n November. Prior to the beginning of experiments, Douglas-fir seedlings which exhibited extremely large crowns as a result of the second flush were discarded. In addition, a l l pots with much greater or much less than average s o i l volumes were discarded to reduce s o i l v a r i a t i o n . Average s o i l volume for this purpose was determined v i s u a l l y . For the experiments, sample seedlings were selected randomly from the remaining treatment populations. Because of the wide range of s o i l water potential expected i n these experiments, s o i l dew-point hygrometers (PT-51, Wescor Inc.) were used i n conjunction with a dew-point microvoltmeter (HT-33, Wescor Inc.) to measure this variable. A l l hygrometer measurements were made i n dew-point mode because of lower s e n s i t i v i t y change with temperature and good agreement with psychrometric mode on plant tissue and s o i l samples (Nnyamah and Black, 1977). /16 One to two days before an experiment, a l l sample seedlings were watered to f i e l d capacity. A 0.3-cm hole was made v e r t i c a l l y into the s o i l , about 1 cm from the root c o l l a r , with a n a i l . A wetted ceramic bulb sensor was then forced into the hole to a point near the middle of each pot and anchored by tape to prevent movement of the sensor during measurements. The pots were then watered again to insure good contact between the sensor bulb and the s o i l . Drainage holes i n the bottom of each pot were taped closed and the s o i l volumes were measured and recorded. Each seedling pot was placed i n a p l a s t i c bag to r e s t r i c t evaporation from the s o i l to a reduced and near constant rate throughout the experiment. A l l bags were closed around the stem i n a similar manner so that vapor pressures would be held within a very narrow, nearly saturated range by the s o i l water potential and high di f f u s i v e resistance of the bag. During experimental periods, but after a day's measurements, the bags were opened every other day for ten mintues to allow for exchange of s o i l atmosphere. This was considered s u f f i c i e n t time since the p l a s t i c bag, when closed, contained a large volume of a i r around the pot and acted as an oxygen reservoir for respiring roots. The p l a s t i c bags and the a i r volume surrounding the pot within the bags acted as a thermal insulator to prevent excessive thermal gradients through the s o i l , thus reducing s o i l water in potential measurement error. Excessive s o i l water potential errors have been demonstrated under large thermal gradients across dew-point hygrometer sensors (Wiebe et al., 1977). 3.3.2 Experimental Environment In the growth chambers,light periods of 15 hours per day were used with a photon fl u x density within the v i s i b l e spectrum -2 -1 of about 450 to 550 uE-m • s at midcrown l e v e l as provided by a bank of incandescent and fluorescent lamps (see Appendix 6). This f l u x density corresponds to about 1/4 of sunlight at f u l l solar noon i n midsummer. Systematic variation of about 20% -2 -1 occurred over the bench. 300 uE*m *s has been determined i n the f i e l d as the intensity at which l i g h t becomes the l i m i t i n g factor to stomatal opening i n 40-year-old Douglas-fir (Tan et al., 1977). No comparable data are available for either hemlock species. Light period temperatures were controlled to 20 ± 1°C. However, the s o i l temperatures were measured to be about 24°C. These s o i l temperatures are not high i n r e l a t i o n to s o i l surface horizon temperatures i n the f i e l d (Isaac, 1938; Herman, 1963; Ballard et al., 1977) even at higher elevations (Brook et al., 1970). Presumably these elevated s o i l temperatures were the result of a greenhouse effect caused by the p l a s t i c bags. Nighttime temperatures were reduced to 15 ± 1°C. The r e l a t i v e humidity was controlled by humidifiers to 65 ± 5% during l i g h t periods and 80 ± 5% during dark periods. /18 Humidity and temperature were recorded continuously by calibrated hygrothermograph and checked regularly throughout a l l experiments. The growth chamber was ventilated at a rate of about 0.35 m-s ^ i n order to minimize changes i n CO2 concentration, reduce boundary layer resistance, and to reduce v a r i a t i o n i n temperature and humidity across the growth chamber bench. Seedlings were systematically arranged, by treatment, to avoid treatment bias due to radiation and v e n t i l a t i o n v a r i a t i o n . 3.4 Experimental and Analytical Procedures 3. 4.1 Water Potential In t h i s study, the needles were considered to be the endpoint of the water uptake flow. Calculation of the water uptake resistance required concurrent measurement of s o i l and needle water potential. Water potential of the s o i l was measured by dew-point hygrometer probes and needle water potential by dew-point hygrometers on excised needles i n sample chambers. Voltage output from the hygrometer microvoltmeter i s l i n e a r l y proportional to the water potential. A l l hygrometers were i n d i v i d u a l l y calibrated and used i n dew-point mode. F i f t y PT-51 s o i l hygrometers were calibrated by immersion into solutions of 0.05, 0.2, 0.3, and 0.5 mol NaCl/kg water representing osmotic potentials of -0.23, -0.9, -1.34, and -2.24 MPa, /19 respectively, at 20 C. A l l solutions were held to 20 C ± 0.02°C by immersion of solution containers i n a constant temperature water bath. Using each sensor, one measurement was made i n each solution to check l i n e a r i t y of ca l i b r a t i o n . Then, four or fi v e measurements were made using these sensors and an additional 50 sensors i n the 0.5 molal solution. The average microvolt output readings were calculated to determine the ca l i b r a t i o n slope for each sensor. Only those sensors which had slopes between 6 and 8 uV-MPa and with less than ± 0.7 uV variation i n output for the four to fi v e measurements i n the 0.5 molal solution were used i n experiments. This variation represents about ± 0.1 MPa at a water potential of 2.2 MPa (for summary, see Appendix 10). Calibration intercepts were determined at the end of experimentation by immersion i n d i s t i l l e d water. This provided both an intercept value, which was very close to zero (see Appendix 10), and a check against possible sensor error. S o i l hygrometer data were recorded i n microvolts and lat e r converted to megapascals. In order to quantify the v a r i a b i l i t y i n s o i l water potential measurements to be expected within a single pot, several seedlings were set up, as described previously, except with two hygrometer sensors placed 2 cm apart on opposite sides of the stem. The seedlings were placed i n the growth chamber and concurrent s o i l water potentials were measured twice a day /20 u n t i l the s o i l dried to about -4 MPa. These data indicated that as much as ± 0.3 MPa variation can be expected within a single pot over the range of about -0.5 to -4.0 MPa s o i l water potential. This variation may be due to (1) inherent sensor equipment and reading error, (2) proximity of sensors to absorbing roots, (3) imperfect integrating power of roots, (4) variable contact between sensor bulb and s o i l , and (5) thermal gradients within the pot. Because of the r e l a t i v e constancy of measured variation as the s o i l dried, sources (1) and (5) may be dominating. Occasional differences of up to 1 MPa measured within one pot might indicate the p o s s i b i l i t y of occasional large error due to (5). Two thermocouple hygrometer sample chambers were used i n these experiments (C-51 and C-52, Wescor Inc.). Each sample chamber was calibrated against known water potentials, using solutions of 0.0, .05, 0.2, 0.3, 0.5, and 0.9 mol NaCl/1 ow water, i n a constant temperature room. The data showed excellent l i n e a r i t y between -0.23 and -4.16 MPa for both sample chambers, and accuracy to within ±0.025 MPa for estimating water potential of the vapor-equilibrated chamber. However, careful technique was necessary to ensure reasonable vapor eq u i l i b r a t i o n with needle tissue which accurately represents water potential conditions i n intact needles immediately before sampling. Vapor eq u i l i b r a t i o n times were p r o h i b i t i v e l y slow (up to several hours) on excised, untreated needles. During such /21 long times, s i g n i f i c a n t changes i n average needle water potential might occur. Two techniques were tested for effectiveness i n reducing vapor eq u i l i b r a t i o n times and producing r e l i a b l e estimates of needle water potential: (1) cutting the excised needles into t h i r d s , crosswise, and (2) wiping the needle surfaces l i g h t l y with a xylene-moistened Kimwipe and cutting into thirds. Cutting the needles with a razor blade was done to expose some water surfaces to the chamber atmosphere to promote evaporation without rupturing a large number of c e l l s . The xylene treatment, used for i t s c u t i c l e solvent a b i l i t y and rapid drying, was performed to increase epidermal evaporation without causing serious damage to tissues, which might change the water potential (Neumann and T h u r t e l l , 1972). The sample chamber holders were coated with melted and r e s o l i d i f i e d paraffin wax, as suggested by Boyer (1967), to reduce water adsorption to the holder surfaces. Tests showed that e q u i l i b r a t i o n with cut needles took about 2 to 3 hours. However, when treated with xylene, e q u i l i b r a t i o n varied from 8 to 40 minutes, but always within 0.2 MPa of the equilibrium value at 20 minutes. The f i n a l equilibrated reading was the same for both treatments, indicating that xylene treatment had no measurable effect on the average water potential of the sampled needles. For subsequent experiments, a 30-minute eq u i l i b r a t i o n time was used. Ill Sample preparation for a l l needle water potential measurements consisted of p u l l i n g off 20 to 30 young needles from the midpoint of a l a t e r a l twig, brushing the needles l i g h t l y with a xylene-moistened brush and quickly wiping the surfaces with a Kimwipe. Within a few seconds, the needle surfaces were dry. The needles were cut into thirds, and the sample holder was f i l l e d with tissue and sealed i n the chamber. This process took about 90 seconds to complete. Speed was c r i t i c a l i n order to prevent s i g n i f i c a n t evaporation from the tissue before sealing inside the chamber, which would cause lower water potentials to be measured. To avoid error caused by contaminants on the hygrometer junction and sample holder, the units were cleaned every other day with acetone or soap and rinsed thoroughly with d i s t i l l e d water. The calibrations were rechecked p e r i o d i c a l l y . Four experimental runs (16 seedlings from each treatment per run) were conducted between September and November, 1976. A l l seedlings were prepared as described previously and placed i n the growth chamber two days before the experiment, to allow diurnal fluctuations to be reduced. Needle water potential and s o i l water potential were measured concurrently on two seedlings from each treatment daily. Only one measurement was taken for each seedling, since the destruction of needles might have had some effect on the seedling's /23 water balance, influencing subsequent measurement. Times of measurement and the sample chamber used were alternated systematically to remove sampling and measurement bias. A l l measurements were taken between 7 1/2 and 10 hours after the beginning of the l i g h t period so that the average time for each treatment was about 8 3/4 hours. F u l l measurement on each pot was about 40 minutes. Each experimental run lasted about eight days. Bags were l e f t open on some seedling pots to f a c i l i t a t e evaporation and thus reduction of s o i l water potentials, but were closed again at least two f u l l days before measurements on those seedlings, in order to allow the s o i l to approach conditions of steady state transpiration and smaller v e r t i c a l gradients of s o i l water potential. From the data obtained by the methods outlined above, the relationship between needle water potential and s o i l water potential was described for each treatment. Since, i n theory, water uptake ceases when the measured needle water potential equals the s o i l water potential, only those data points within the s o i l water potential range where IJJ < \\> were included i n a N s regression to define a relationship i n the range where si g n i f i c a n t water uptake occurred. A simple covariance analysis was performed to test for differences between treatments (Osborn et al., 1972). /24 Using the above regression equations the relationships between water potential difference (between s o i l and needles) and s o i l water potential for each treatment were calculated and compared over the s o i l water potential range where signficant water uptake occurred. 3.4.2 Water Uptake Rate Average water uptake rates for each treatment were calculated from weight loss data measured concurrently with s o i l water potential. Two runs of 7 or 8 seedlings from each treatment were conducted between July and September, 1976. The seedlings were prepared as described i n a previous section, and placed i n the growth chamber two days before measurements began. Weight loss rates were determined during subsequent l i g h t periods by weighing each pot three times d a i l y , (beginning four hours af t e r the start of the l i g h t period) at 9:30, 1:30 and 5:30, on a 0.05•g-division top-loading balance. This permitted calculation of the average weight loss rate for each seedling over two four-hour periods each day. S o i l water potential measurements, taken concurrently with weighings, were averaged to produce the corresponding average s o i l water potential over each period. The measurements were continued d a i l y , on each seedling, u n t i l the s o i l water potential was consistently measured at less than -4.0 MPa for Douglas-fir and -3.5 MPa for the hemlocks. This period varied between 10 and 20 days, depending upon the treatment and seedling. 125 Water uptake rates are d i r e c t l y affected by the influence of seedling size on the dimensions of the water flow pathway. Since the l i m i t i n g resistances to uptake and loss generally appear to occur i n the regions of the roots and the leaves of plants, information concerning pathway dimensions i n these regions was considered to be useful for analysis of water uptake data among seedlings and treatments. Therefore, for each seedling used i n the weight loss rate experiments, estimations were made of (1) needle surface area, (2) root surface area and length, and (3) extent of mycorrhizal infection and root hair development. Needle surface areas (one-sided) of each seedling were calculated by measuring the oven-dry mass of a l l needles (16 hours at 80°C) and multiplying by the r a t i o of needle surface area to oven-dry mass, determined for each species. These ratios were determined by excising a l l needles from four seedlings of each species, and carefully laying the needles as closely together as possible, without overlap, on s l i g h t l y adhesive graph paper with a 1-mm grid. The areas for each seedling were recorded and the needles carefully removed and oven-dried. The average r a t i o for each species was calculated from these data (see Appendix 7 for values). These cross-sectional areas of segments of the water uptake pathway i n the region of the roots outside the xylem are /26 proportional to the root surface area (Gardner, 1960). The path length of water flow i s dependent upon root d i s t r i b u t i o n as determined by the distance between absorbing roots. This distance tends to be inversely proportional to the t o t a l length of roots within the s o i l volume. length for each seedling, the roots were assumed to be approximately c y l i n d r i c a l within narrow ranges of diameter, and evenly distributed throughout the s o i l volume. A l l roots were assumed to be equally permeable to water. Fresh root surface area (A) can be calculated by where r i s the average fresh root radius and 1 i s the average length of fresh roots. Likewise, fresh root volume (V) In order to calculate root surface area and root A = 2-rrrl (3) V = T r r 2 l (4) and since fresh root density ( p ) i s m (5) where m i s the fresh root mass, then Ill Three root radius classes were distinguished: 0.5 mm to stem base radius, 0.25 to 0.5 mm, and 0 mm to 0.25 mm. The average radius (r) of each size class was calculated from these range values. Fresh root tissue densities were obtained for each species and size class by f l o t a t i o n i n f l u i d s of different density (see Appendix 7). A l l root densities -3 ranged between 950 and 1080 kg-m Fresh root mass was determined after the f i n a l weight loss measurements were taken for each seedling (at ip of about -3.5 to -4.0 MPa). The s o i l around the roots was l i g h t l y crumbled free of the roots and then l i g h t l y sieved to remove broken roots. A l l roots were carefully washed i n water and blotted dry. Using a d i a l c a l i p e r and small scissors, the roots were cut into the three size classes. By the time this was done (30 minutes), the root surfaces were dry, presumably to a moisture condition similar to the undisturbed plant roots, and so represent an average degree of hydration i n the roots l i k e those of the undisturbed seedling during the weight loss experiment. The roots were then weighed to arrive at the mass of the fresh roots (m). Root surface areas were calculated for each size class and summed to produce the t o t a l root surface area for the seedling. In a l l cases, more than 80% of the t o t a l seedling root surface area was provided by the smallest radius class. /28 The root length was calculated by 1 = ^ 2 ( 7 ) p u r for each size class, and summed to produce the t o t a l root length for the seedling. From the above data, additional calculations were made to further describe the water uptake pathway near the roots. By weighting the average r a d i i of the size classes by the length of roots i n each size class r e l a t i v e to the t o t a l , and then summing,the average root radius for the seedling (r^) was obtained. h h x3 r = ( T - L - ) r 1 + ( y ^ ) r 2 + (37^—)^ (8) t o t a l t o t a l t o t a l Assuming that the roots were equally distributed throughout the t o t a l measured s o i l volume, the equation V 1 n = (9) i s obtained, where 1 i s the t o t a l root length for the seedling, V i s the volume of s o i l , and n becomes the closest distance s between root centers. The point farthest from an adjacent root center i s located 2 (n/2) from the root center. It i s /29 assumed, for purposes of calculation, that ip g i s measured at a point halfway between that furthest point and the adjacent root center, i.e. at a distance s = 2l2(n/4) = (V /81 ) h (10) s t from the root center. Theoretically, s approximately represents the average direct distance water must tr a v e l from the point where \b i s T s measured to the point where i t enters the xylem. By subtracting the average radius (r^) of the root system from the value s, z = s - r (11) one obtains an estimate of the pathlength (z) through the s o i l to the seedling root surface, from the point where i s measured. Calculated values of z for various treatments have no absolute meaning, because of underlying assumptions. However, they enable some comparison of r e l a t i v e pathlengths of water movement through the s o i l (see Appendix 8 for summary of calculated values). A l l parts of the seedling were oven-dried to calculate root:shoot dry mass r a t i o s . The r e l a t i v e abundance of root hairs and abundance of mycorrhizal hyphae were noted for each treatment, as they might influence water flow resistance at the root surface. /30 From weight loss rate data for each seedling, a non-linear least squares curve f i t , by stepwise Gauss-Newton i t e r a t i o n s , was produced for each seedling to y i e l d an equation for weight loss rate (W) in re l a t i o n to s o i l water potential. The equation W = d + ab (^s " c) (12) was found to f i t a l l seedlings reasonably w e l l . The asymptotic d value was assumed to approximate the evaporation rate from the bag and was subtracted to y i e l d the water uptake rate (U) for each seedling. Water uptake rates were expressed on the unit root surface area basis: In an attempt to reduce var i a t i o n for seedlings within treatments, W - d a b ^ 8 " c ) u - h r ^ = A — ( 1 3 ) r r Using equation 13 equal numbers of equally distributed points were calculated for each seedling over the s o i l water potential range of -0.4 to -4.0 MPa. These generated data points for a l l seedlings within a treatment were then f i t t e d by equation 14 to produce the treatment average water uptake rate per root area, in r e l a t i o n to s o i l water pot e n t i a l : U = e f ( ^ s - g ) (14) The above procedure was performed to reduce bias toward seedlings of particular water uptake behavior. Seedlings which /31 were slow to reach -4.0 MPa s o i l water potential had more data points collected and this slower rate might have been due to seedling size differences. These seedlings also tended to have disproportionately more data points i n the wet end of the s o i l water potential range. Several seedlings, especially those with very fast water uptake rates, had no data i n the very wet end. Therefore, i t was f e l t that the treatment water uptake rate i n r e l a t i o n to s o i l water potential, and hence, the resistance to water uptake can be accurately described only to an upper l i m i t of about -0.5 MPa s o i l water potential. The above calculation procedure presented a p r o h i b i t i v e l y complex s t a t i s t i c a l problem. Therefore, to simplify, analyses of variance of generated data points at -0.6 and -2.0 MPa were performed as a rough test for differences between treatments (for summary see Appendix 9). The close f i t of indiv i d u a l seedling data to equation (12) and low variation among these data lend additional support to th i s kind of analysis. However, considerable v a r i a t i o n among seedlings within treatments was expected and observed. Having calculated the water uptake rate per unit root surface area i n r e l a t i o n to s o i l water potential for each treatment, m u l t i p l i c a t i o n by the treatment average seedling root surface area produced the treatment average water uptake rate per seedling i n r e l a t i o n to s o i l water potential. /32 3.4.3 Resistance By equation 2 (Chapter 2), the average resistance to water uptake was calculated over the s o i l water potential range of -0.5 MPa to about -2.5 to -3.2 MPa, depending upon the value of s o i l water potential where the water potential difference i s about zero. This measure of resistance afforded a useful comparison of treatments i f the pathway dimensions were sim i l a r . However, when th i s condition was not met, the resistance was calculated on a root surface area basis to provide a more r e a l i s t i c basis of comparison. /33 CHAPTER 4: RESULTS AND DISCUSSION: SOILS 4.1 Water Potential Needle water potential for Douglas-fir seedlings does not change much with decreasing s o i l water potential over the range where s i g n i f i c a n t water uptake occurs, down to i|> of about -2.5 MPa. Needle water potentials for a l l three s o i l s remain at about -2.5 MPa to -2.7 MPa over this range (Figures l a , b, and c). Beyond this range, continual water loss from the plant, without compensating water uptake, causes needle water potential to decline. A comparison of s o i l s i n Figure 2 shows that i n s i l t loam, and more so i n loamy sand, there i s a s l i g h t decline i n needle water potential with decreasing s o i l water po t e n t i a l , a result which would be consistent with the lower unsaturated hydraulic conductivities and consequently higher uptake resistances that one might expect at low s o i l water potentials i n coarse-textured s o i l s . However, despite apparent differences between these l i n e s , there were 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 differences. Since the relationships between needle water potential and s o i l water potential have slopes very near zero, the water potential difference between s o i l and needle i s a v i r t u a l l y linear function of s o i l water potential above about -2.7 MPa i n these experiments (Figure 4. 2 Water Uptake Rate In order to reduce v a r i a t i o n , water uptake rates were expressed on a per unit root area, per needle area, as well as /34 per seedling basis. In Figures 4a, b, and c each series of data points represents an individual seedling. Although expression on a root area basis reduced variation somewhat, considerable variation remains at the wet end of the graph. Expression on a needle area basis was no better. Since no consistent relationships were found between individual seedling dimensions and their corresponding water uptake rates, i t i s inferred that much of this variation i n water uptake per unit root area may be due to differences in irradiance and v e n t i l a t i o n across the growth chamber bench as well as physiological variation within this provenance. Water uptake rate per unit root area decreased rapidly i n a l l s o i l s as the s o i l dried from about -0.5 MPa to about -2.5 MPa, and did not approach zero u n t i l about -3.0 MPa. The major reason that the uptake rate did not approach zero u n t i l well below equilibrium conditions (that i s , when needle water potential equalled s o i l water potential) appears to be a result of the r e l a t i v e inaccuracy of equation 12 to describe the water uptake data below about -2.2 MPa s o i l water potential. Observations of the graphic data and curve output for each seedling show a smoothing tendency by the curve produced by equation 12 which does not precisely describe the more abrupt l e v e l l i n g off behavior of the uptake rate data below about -2.2 MPa. There appears to be a consistent s l i g h t overestimation of water uptake rate per unit root area, by the curve, between -2.2 and -2.8 MPa, and a consistent underestimation below about -2.8 MPa. Thus, the asymptotic values (d) of the curves are almost certainly /35 underestimates of the evaporation rate from the bag, and water uptake rates per unit root area between -2.2 MPa and -2.8 MPa are s l i g h t l y overestimated. However, th i s error i s not so serious that i t changes the resistance results materially over other parts of the s o i l water potential range. Despite the observed v a r i a t i o n i n Figures 4a, b, and c, s i l t y clay was s i g n i f i c a n t l y different (p = .01) from loamy sand at the wet end of the curve (Figure 5). S i l t loam behaved intermediately to s i l t y clay and loamy sand, which was expected from s o i l unsaturated hydraulic conductivity characteristics. However, s i l t loam was not s i g n i f i c a n t l y different from the other textures. There were no sign i f i c a n t differences between curves at -2.0 MPa. The curves of average seedling water uptake rate (Figure 6) are very similar to those of average seedling water uptake rate per unit root surface area, due to very similar average root surface areas between treatments. The uptake rate for s i l t y clay i s about 15% higher than for s i l t loam and about 40% higher than for loamy sand. The proportions remain similar over much of the s o i l water potential range. 4. 3 Resistance For a l l three s o i l textures, the average seedling resistance to water uptake changed very l i t t l e with decreasing s o i l water potential between -0.5 and -1.0 MPa (Figure 7). This agrees well with Nnyamah's observations on 20-year-old Douglas-fir i n the f i e l d (Nnyamah et al., 1978). /36 With declining s o i l water potential from -1.0 to -2.2 MPa, resistance increased about 2-fold. Loamy sand, with s l i g h t l y higher water potential differences and much lower uptake rates, consistently yielded the highest resistance, and s i l t y clay, with lower water potential difference and much higher uptake rates, yielded the lowest resistance at a l l s o i l water potentials. S i l t loam was consistently intermediate. The resistance i n loamy sand i s almost twice that of s i l t y clay at -0.5 MPa and increases more rapidly, as the s o i l dries, than for s i l t y clay. Below about -2.2 MPa, i n a l l three s o i l s , the calculated resistance decreases rapidly. This decrease i s probably an a r t i f a c t resulting from the overestimate of water uptake at the very dry end. This overestimate becomes r e l a t i v e l y very large as the s o i l dries below -2.2 MPa. Calculations based upon water uptake f a l l i n g to zero when water potential difference equals zero, show a consistent increase i n resistance i n t his range, which probably represents a more accurate description. 4.4 Discussion Douglas-fir seedling water stress, as indicated by the needle water p o t e n t i a l , i s not much affected by s o i l drying down to about -2.7 MPa, so long as water can flow into the plant. Thus, these seedlings appear well able to regulate their water balance, to maintain almost constant needle water potential, so long as there i s a si g n i f i c a n t rate of water flow into the seedlings. /37 However, the resistance to this flow increases greatly as the s o i l dries below about -1.0 MPa. Because root surface areas, root lengths, and s o i l volumes are similar for a l l three s o i l textures, i t i s inferred that unsaturated hydraulic conductivity of the s o i l and, perhaps, the s o i l - r o o t contact, are major contributing factors to differences i n resistance among the three s o i l s . The ranking of textures i n terms of resistance i s predictable from their ranking i n terms of unsaturated hydraulic conductivity. Texture apparently does influence water flow resistance and hence influences the rate of water uptake by the seedling. The differences i n resistance and uptake rate may be very large i n moderately dry s o i l s of different texture. However, the resistance i n the plant component of the flow pathway i s extremely important i n the t o t a l resistance. As s o i l unsaturated hydraulic conductivity i s known to change considerably between -0.5 and -1.0 MPa (Gardner, 1960), the lack of change i n resistance, found i n this study, over t h i s range suggests that at higher s o i l water potentials (up to -0.5 MPa) the plant resistance, and perhaps the s o i l - r o o t contact resistance, dominate the t o t a l resistance. Calculations based upon Gardner's (1960) water flow model through s o i l to absorbing roots and using his values for unsaturated hydraulic conductivity for a loam s o i l (but substituting values determined i n t h i s study for seedling average t o t a l root length (l t)> root radius (r^) and distance from hygrometer sensor to the root center (s), indicate that s o i l resistance i s about an order of magnitude /38 less than t o t a l resistance i n this range. These results appear to agree with Newman's (1969b) argument that s o i l resistance remains small u n t i l the s o i l becomes quite dry. This might indicate important r o o t - s o i l contact resistance differences between s o i l s which account, to a large degree, for differences i n t o t a l resistance to water uptake i n this s o i l water potential range. Because mycorrhizal mantles surrounding roots of these seedlings were observed to be only s l i g h t on s i l t y clay and very s l i g h t on s i l t loam and loamy sand, and because contact resistance perhaps may affect water movement to hyphae, mycorrhizae are not considered to affect these results materially. SOIL WATER POTENTIAL ( MAPA ) -9.0 -8.0 -7.0 -B.O -5.0 -4.0 -3.0 I I -I I 1 1 1 -2.0 -1.0 _ l 0.0_ B B / • . —* 1 cr a. a i w »* 5 = r-/ / / / / / / / .mLU ' I— O Q_ Ct LU o l — i UJ i a LU . 10 I FIGURE l a : Needle water potential i n r e l a t i o n to s o i l water potential for Douglas-fir on s i l t y clay s o i l . SOIL WATER POTENTIAL: ( MAPA ) -9.0 -B.0 -7.0 -6.0 -5.0 -4.0 -3.0 I I I I I I 1 -2.0 - 1 . 0 _ l CO-FIGURE l b : Needle water potential i n r e l a t i o n to s o i l water potential for Douglas-fir on s i l t loam s o i l . -9.0 -8.0 _1 SOIL WATER POTENTIAL C MAPA J -7.0 -B.0 -5.0 -4.0 -3.0 -2.0 J I I 1 1 1 -1.0 0.0^ / / cc a. cc . C N w I .mLU i h— ED Q_ CC UJ Oh-i ^ UJ a U J . in i .(£> I FIGURE l c : Needle water potential i n rela t i o n to s o i l water potential for Douglas-fir on loamy sand s o i l . M2 SOIL WATER POTENTIAL ( MflPA ) -4.0 -3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 O.OL I 1 1 I I I I I ' ° i i (X a. in 2= I ex .roLU • h -Q Q. QC LU inh-i LU _ J a LU a L U .rn i .rn i FIGURE 2: Needle water potential i n r e l a t i o n to s o i l water potential for Douglas-fir: A comparison of s o i l s ; s i l t y clay (SiC), s i l t loam (SiL) and loamy sand (LS). /43 FIGURE 3: Water potential difference i n r e l a t i o n to s o i l water potential for Douglas-fir: A comparison of s o i l s ; s i l t y clay (SiC), s i l t loam (SiL) and loamy sand (LS). Ikk -4.0 -3.0 -2.5 -2.0 SOIL WATER POTENTIAL FIGURE 4a. Average seedling water uptake rate per unit root surface area i n r e l a t i o n to s o i l water potential for Douglas-fir on s i l t y clay s o i l . This relationship was arrived at through equation 14. /45 FIGURE 4b: Average seedling water uptake rate per unit root surface area i n r e l a t i o n to s o i l water potential for Douglas-fir on s i l t loam s o i l . This relationship was arrived at through equation 14. /46 -4.0 -3.5 -3.0 -2.5 -2.0 SOIL WATER POTENTIAL T ~ *— r -1.5 -1.0 ( MRPfl ) -0.5 0.0 FIGURE 4c: Average seedling water uptake rate per unit root surface area i n r e l a t i o n to s o i l water potential for Douglas-fir on loamy sand s o i l . This relationship was arrived at through equation 14. /47 FIGURE 5: Average seedling water uptake rate per unit root surface area i n r e l a t i o n to s o i l water potential for Douglas-fir A comparison of s o i l s ; s i l t y clay (SiC), s i l t loam (SiL) and loamy sand (LS). /48 FIGURE 6: Average seedling water uptake rate in r e l a t i o n to s o i l water potential for Douglas-fir: A comparison of s o i l s ; s i l t y clay (SiC), s i l t loam (SiL) and loamy sand (LS). /49 — a — r-— in -ro FIGURE 7: Average seedling water uptake resistance i n r e l a t i o n to s o i l water potential for Douglas-fir: A comparison of s o i l s ; s i l t y clay (SiC), s i l t loam (SiL) and loamy sand (LS). The decrease i n resistance below about -2.2 megapascals i s probably an a r t i f a c t of the calculation process. /50 CHAPTER 5: RESULTS AND DISCUSSION: SPECIES 5.1 Water Potential Difference Unlike Douglas-fir, both western and mountain hemlock show a r e l a t i v e l y large decrease i n needle water potential as the s o i l dries from near zero to about -3.0 MPa (Figures 8a, b, and c). Western hemlock shows s l i g h t l y less tendency to change than mountain hemlock. As with Douglas-fir, t h i s relationship appears to be a li n e a r function of s o i l water potential over t h i s range. A comparison of species (Figure 9) shows that both hemlocks appear less able to maintain near-constant needle water potentials than Douglas-fir as the s o i l dries to about -3.0 MPa. Douglas-fir i s s i g n i f i c a n t l y different (p = .01) from both hemlock species, and the two hemlock species also d i f f e r s i g n i f i c a n t l y (p = .05). Since the relationship between s o i l water potential and needle water potential i s approximately linear with slopes less than 1, the water potential differences decrease as the s o i l dries down to about -2.7 to -3.3 MPa i n these experiments (Figure 10). However, mountain hemlock shows consistently the lowest water potential difference and Douglas-fir the highest, down to about -1.8 MPa, where the curves cross. Western hemlock i s intermediate at a l l s o i l water potentials. 5. 2 Water Uptake Rate Average seedling water uptake rates per unit root surface area for both hemlock species were much lower than for Douglas-fir at /51 a l l s o i l water potentials and decreased as the s o i l dried, approaching zero at -2.5 MPa s o i l water potential (Figures 11a, b, and c). Mountain hemlock consistently showed the lowest uptake rate over t h i s range (Figure 12). A l l li n e s were s i g n i f i c a n t l y different (p = .01) from each other at ^ g = -0.6 MPa. At *pg = -2.0 MPa, Douglas-fir was s i g n i f i c a n t l y different (p = .01) from either hemlock species, but there i s no s i g n i f i c a n t difference between hemlock species. Comparison of average seedling water uptake rate per unit root surface area (Figure 12) and average seedling water uptake rate (Figure 13) show similar trends. However, there i s a lesser difference between species on a seedling basis because the hemlock species have much more root surface area per seedling. At -0.5 MPa, the Douglas-fir average seedling water uptake rate i s 44% higher than for western hemlock and 53% higher than for mountain hemlock. These proportions remain f a i r l y similar over the f u l l s o i l water potential range. It i s very interesting to note that although mountain hemlock has the highest root surface area (on the average, almost twice that of Douglas-fir), i t shows only half the water uptake rate. S i m i l a r l y , western hemlock has about 1.5 times the root area of Douglas-fir, and shows only 44% of the water uptake rate i n wetter s o i l . In addition, both hemlock species have 20% greater needle surface area than for Douglas-fir. Apparently the resistance to water uptake by both hemlock species i s s u f f i c i e n t l y larger to offset their larger absorbing and transpiring surfaces r e l a t i v e to Douglas-fir. 152 5. 3 Resistance For a l l three species, the average seedling water uptake resistance changes slowly between -0.5 and -1.0 MPa, but increases at an increasing rate as the s o i l dries below -1.0 MPa (Figure 14). In Douglas-fir, the increase i s about 2-fold between -0.5 and -2.5 MPa. However, the increase i n resistance i s about 10- and 20-fold for western and mountain hemlock, respectively. At \Li above -1.8 MPa, the lower water potential differences s and much lower water uptake rates i n the hemlocks r e f l e c t uptake resistances that are 2 to 3 times that for Douglas-fir. Below this range, extremely small water uptake i n response to higher water potential differences i n hemlocks than Douglas-fir, r e f l e c t s resistance differences of up to a f u l l order of magnitude. Western hemlock i s intermediate between mountain hemlock (with the highest resistance) and Douglas-fir (with the lowest resistance) at a l l s o i l water potentials. Since a l l three species show markedly different root surface areas, the uptake resistance i s calculated on a root surface area basis, to offer clearer comparison (Figure 15). Because the root surface area of Douglas-fir i s lowest and that of mountain hemlock i s highest, the resistance to water uptake on a root area basis shows much larger differences between species than when expressed on a seedling basis. Evidently, there i s dramatically higher resistance to water uptake, through comparable areas of roots, for hemlocks than for Douglas-fir. /53 As previously noted, decrease i n resistance i n the very dry end i s considered to be an a r t i f a c t of the calculation processes and i s much smaller for the hemlocks than for Douglas-fir. 5.4 Discussion Unlike Douglas-fir, both western and mountain hemlock appear less able to control needle water potential as the s o i l dries. Needle water potential for both hemlocks decreases about 1.0 MPa from s o i l water potential of near zero down to about -3.0 MPa where needle water potential becomes equal to s o i l water potential, whereas Douglas-fir maintains almost constant needle water potential down to about -2.7 MPa. In theory, these values represent the lower l i m i t of s o i l dryness for water uptake by these species (at lea s t , under these experimental conditions). However, the resistance to water uptake increases as the s o i l dries, and hence, the water uptake f l u x decreases more rapidly than can be accounted for simply by a decrease i n water potential differences. The data suggest that the resistance i n hemlocks becomes so large, as the s o i l water potential decreases, that the uptake rate decreases to near zero i n s o i l almost 1.0 MPa wetter than -3.0 MPa (the \i> value where ip - ij> becomes equal to zero). The resistance i s s s N much smaller i n Douglas-fir, which shows a s i g n i f i c a n t water uptake rate over the f u l l range of s o i l water potential where water potential differences e x i s t . Because root surface areas and root lengths are much larger for both hemlocks than for Douglas-fir, and s o i l volumes are s i m i l a r , i t i s inferred that the plant tissue, and perhaps /54 soi l - r o o t contact, are major factors contributing to differences i n resistance between species. Because both hemlock species have higher root surface areas and root lengths than Douglas-fir, the resistance to water flow through the s o i l to the root i s less than for Douglas-fir. In view of the low s o i l resistance, as mentioned i n the previous chapter, calculated by Gardner's model, the plant tissue and perhaps the s o i l - r o o t contact resistances are dominating the t o t a l resistance, at least i n the wet end. The so i l - r o o t contact, which, in the same s o i l , i s affected by the morphology of the root surfaces, might play an important role i n causing differences i n t o t a l resistance between species. I t was noted that Douglas-fir develops a large number of l a t e r a l root hairs, about 0.5 to 1.0 mm long, over a l l roots smaller than 1.0 mm i n diameter. I t i s possible that this morphological characteristic may be advantageous to the seedling, for keeping i n close contact with s o i l water films as the s o i l dries, as well as decreasing the effective distance water must travel to the root surface and increasing the t o t a l absorbing root surface area. The s l i g h t mycorrhizal in f e c t i o n on some Douglas-fir roots might also have similar effect. Although ectomycorrhizal mantles, common to conifer species, appear to suppress or cover root hairs i n regions where mantles form (Harley, 1969), the physical presence of the thick mantle and hyphae may help to maintain close contact with s o i l water films i n a similar manner as root hairs on 155 nonmycorrhizal roots. However, both hemlock species were observed to have neither s i g n i f i c a n t root hair development nor perceptible mycorrhizae association. This condition might explain, to a large degree, the hemlock's larger and more rapidly increasing resistance differences r e l a t i v e to Douglas-fir as the s o i l dries. Since western hemlock uptake resistance i s less than that for mountain hemlock, even though there i s less absorbing surface area and larger average distance between roots, i t i s inferred that the resistance to water uptake through the plant tissues of western hemlock i s lower than for mountain hemlock at a given s o i l water potential. For hemlocks, the p r o l i f e r a t i o n of roots through the s o i l s , as found i n these experiments, might be of considerable ecological importance i f much of the water uptake resistance occurs i n the region of the roots. In the absence of root hairs, p r o l i f e r a t i o n of fine roots may reduce water uptake resistance through s o i l and across the root in a similar manner as root hairs. Although t h i s cannot be concluded i n this study, i t does indicate an interesting trend. \ -9.0 I -8.0 SOIL WATER POTENTIRL ( MRPfl ) 7.0 -6.0 -5.0 -4.0 -3.0 J I 1 I 1 -2.0 -1.0 _ l FIGURE 8a. Needle water potential in rela t i o n to s o i l water potential for Douglas-fir on s i l t loam s o i l . (same as Figure lb) FIGURE 8b: Needle water potential i n relation to s o i l water potential for western hemlock on s i l t loam s o i l . FIGURE 8c: Needle water potential i n rel a t i o n to s o i l water potential for mountain hemlock on s i l t loam s o i l . /59 SOIL WATER POTENTIAL ( MAPA ) -4.0 -3.5 -3.0 -2.5 -2.0 -1.5 -1.0 I 1 1 1 I I I -0.5 0.0_ in CD _ i—( I cr Q_ cr cr i—i . r\juJ ' (— £D Q_ cr LU in I— i _s LU I a 3LU .rn i . rn i FIGURE 9: Needle water potential i n r e l a t i o n to s o i l water potential for seedlings on s i l t loam s o i l : A comparison of species; • Douglas-fir (DF), western hemlock (WH) and mountain hemlock (MH). FIGURE 10: Water potential difference i n r e l a t i o n to s o i l water potential for seedlings on s i l t loam s o i l : A comparison of species; Douglas-fir (DF) , western hemlock (WH) and mountain hemlock (MH). /61 FIGURE 11a: Average seedling water uptake rate per unit root surface area i n r e l a t i o n to s o i l water potential for Douglas-fir on s i l t loam s o i l . This relationship was arrived at through equation 14. /62 -4.0 -3.5 -3.0 -2.5 -2.0 SOIL WATER POTENTIRL T" r -1.5 -1.0 ( MAPA ) T -0.5 .OJ .dco C o d LU CC O KnCe 0.0 FIGURE l i b : Average seedling water uptake rate per unit root surface area in r e l a t i o n to s o i l water potential for western hemlock on s i l t loam s o i l . This relationship was arrived at through equation 14. /63 FIGURE 11c: Average seedling water uptake rate per unit root surface area i n r e l a t i o n to s o i l water potential for mountain hemlock on s i l t loam s o i l . This relationship was arrived at through equation 14. /64 FIGURE 12: Average seedling water uptake rate per unit root surface area i n r e l a t i o n to s o i l water potential for seedlings on s i l t loam s o i l : A comparison of species; Douglas-fir (DF), western hemlock (WH) and mountain hemlock (MH). /65 i IT) FIGURE 13: Average seedling water uptake rate i n r e l a t i o n to s o i l water potential for seedlings on s i l t loam s o i l : A comparison of species; Douglas-fir (DF), western hemlock (WH) and mountain hemlock (MH). /66 - o • r-• in |-cn CD LO CL - ^ L U :°<-> • -z. - r-tr - t — - to LU -roCe: LU - ^ cn —I f MRPR -4.0 -3.5 -3.0 SOIL -2.5 WATER POTENTIAL -1.0 -0.5 0.D FIGURE 14: Average seedling water uptake resistance i n r e l a t i o n to s o i l water potential for seedlings on s i l t loam s o i l : A comparison of species; Douglas-fir (DF), western hemlock (WH) and mountain hemlock (MH). The decrease in resistance i n the very dry end i s probably an a r t i f a c t of the calculation process. I 1 1 1 1 1 I I -4.0 -3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 SOIL WATER POTENTIAL ( MAPA ) FIGURE 15: Average seedling water uptake resistance on a unit root surface area basis i n r e l a t i o n to s o i l water potential for seedlings on s i l t loam s o i l : A comparison of species; Douglas-fir (DF), western hemlock (WH) and mountain hemlock (MH). The decrease i n resistance i n the very dry end i s probably an a r t i f a c t of the calculation process. /68 CHAPTER 6: SUMMARY AND CONCLUSIONS In t h i s study, the resistance to water uptake from the s o i l to the needles, for a l l three species and on a l l three s o i l s , increases as the s o i l dries. That i s , water uptake rates decrease faster than can be explained simply by the reduction of water potential difference between s o i l and needles. This i s i n agreement with the l i t e r a t u r e for a variety of herbaceous species and some woody plants. The t o t a l resistance to water uptake by Douglas-fir i s higher and increases more rapidly with s o i l drying for seedlings rooted i n coarser textured s o i l than i n fi n e r textured s o i l . While, for Douglas-fir, the higher resistance i n coarse s o i l s does not s i g n i f i c a n t l y influence the seedling water potential i n r e l a t i o n to s o i l water pot e n t i a l , i t does result i n substantially lower water uptake rates over the s o i l water potential range of -0.5 to -2.5 MPa. The effect of texture on resistance appears to result from lower unsaturated hydraulic conductivity of s o i l and poorer s o i l - r o o t contact i n coarser s o i l at a given s o i l water potential. Thus, texture does influence the t o t a l resistance to water uptake, and hence, influences the rate of water uptake by the seedling. Rough calculations suggest that the resistance i n the s o i l portion of the pathway i s probably not large, r e l a t i v e to the t o t a l , u n t i l the s o i l dries to below -2.0 MPa, i n th i s study where root densities are high. /69 In the same s o i l , Douglas-fir seedlings have a much lower resistance to water uptake than both western hemlock and mountain hemlock. The resistance i n hemlocks becomes so high, as the s o i l d r i e s , that water uptake i s reduced to near zero by -2.0 MPa, almost 1.0 MPa above the point where s o i l water potential becomes equal to needle water potential. Higher plant tissue and, perhaps, s o i l - r o o t contact resistances i n western and mountain hemlock than i n Douglas-fir may account for these obvious differences i n t o t a l resistance. Thus, i n this study, there are large differences between Douglas-fir seedlings and western and mountain hemlock seedlings i n their water stress and water uptake characteristics. 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Taylor, H. M. and B. Klepper. 1975. Water uptake by cotton root systems: An examination of assumptions i n the single root model. S o i l Science 120: 57-67. T i n k l i n , R. and P. E. Weaterhley. 1966. On the relationship between transpiration rate and leaf water potential. New Phytol. 65: 509-517. Utzig, G. and L. Herring. 1974. Factors s i g n i f i c a n t to high elevation forest management. B.C.F.S. Res. Div. Exp. Project 735. van den Honert, T. H. 1948. Water transport i n plants as a catenary process. Discussions of the Foraday Society No. 3: 146-153. Van Eerden, E. 1974. Growing season production of western conifers. In: R. W. Tinus, W. I. Stein and W. E. Balmer (eds.). Proc. North American containerized forest tree seedling symposium. 1974. Great Plains Agric. Council Publ. No. 68. p. 93-103. Waring, R. H. 1970. Matching species to s i t e . In: R. K. Hermann (ed.) Proc. Regeneration of Ponderosa pine. For. Res. Lab, Sch. For., Oregon State Univ., C o r v a l l i s . p. 54-61. Wiebe, H. H., R. W. Brown and J. Barker. 1977. Temperature gradient effects on in situ hygrometer measurements of water potent i a l . Agronomy J. 69: 933-939. 115 APPENDICES Page 1. Hoagland's Nutrient Solution, Modified 76 2. Seedling Provenances 77 3. S o i l Properties 78 4. S o i l P a rticle-Size D i s t r i b u t i o n 79 5. S o i l Water Retention Curves 80 6. Growth Chamber Photon Flux Densities 81 7. Fresh Root Tissue Densities and Needle Area: Oven-dry Weight Ratios 82 8. Seedling and Water Flow Pathway Dimensions 83 9. Summary of Analysis of Variance of Seedling Water Uptake Rate per Unit Root Surface Area 84 10. Sample Chamber and S o i l Hygrometer Calibration Information 85 APPENDIX 1: Hoagland's Nutrient Solution, Modified Mass Dissolved i n ml Solution/Liter Salt 1 L i t e r H„0 (g) F u l l Strength NH 4H 2P0 4 115 1 KN03 202 3 Ca(N0 3) 2-4H 20 315 4 MgS04'7H20 164 3 H 3B0 3 2.86 1 MnCl2-4H20 1.81 1 ZnSO,•7H„0 4 2 .22 1 CuSO.-5H.0 4 I .08 1 (NH 4) 6Mo 70 2 4'H 20 .02 1 Ill APPENDIX 2: SEEDLING PROVENANCES Douglas-fir Latitude: Longitude: B.C.F.S. Seed Lot Ident, No. 48° 50' 123 48' 92B13/B2/315/1.5 Western hemlock Latitude Longitude B.C.F.S. Seed Lot Ident. No. 49° 40' 123 50' 92H11/B3/2476/112B Mountain hemlock Latitude Longitude B.C.F.S. Seed Lot Ident. No. 49° 40' 121 u 20' 92G5/B3/2368/1097 /78 APPENDIX 3: SOIL PROPERTIES S o i l % Sand a % S i l t a % Clay a % 0Mb K S i l t y Clay 12 42 46 13.3 4.5 6.3d S i l t Loam 39 52 9 9.8 4.9 15. 3 e Loamy Sand 84 12 4 2.4 5.0 130.4e Percentages based upon 2 mm and smaller fraction by hydrometer method. by Walkley-Black method. C l : 5 Soil:Water ^Unsaturated hydraulic conductivity at 12 cm tension by tensiometer-outflow method (cm day--'-). Unsaturated hydraulic conductivity at 22 cm tension by tensiometer-outflow method (cm day--'-). NOMINAL PARTICLE DIAMETER f N/1) /80 APPENDIX 5: Water Retention Curves for S i l t y Clay (SiC), S i l t Loam (SiL) and Loamy Sand (LS). ( i'<"cW/"-"£w ) 1N31N0D 83±V/*\ DIcLGWfnOA i APPENDIX 6: Photon Flux Densities Across the Growth Chamber Bench^ Growth Chamber 1 Growth Chamber 2 450 480 460 450 480 460 510 550 510 91 cm 510 530 510 470 480 460 460 470 460 < 130 cm y Measured by Quantum Radiometer i n .4 - .7 pm spectrum i n uE-m -2. s-l a t midcrown l e v e l . /82 APPENDIX 7: Fresh Root Tissue D e n s i t i e s 8 and Needle Area: Oven-dry Weight Ratios Root Diameter Class Needle Area: 2 .5 mm - .5-1.0 mm 1.0 mm + Dry wt. (cm /g) Douglas-fir 1.04 .95 1.03 140 Western hemlock 1.08 1.08 1.00 117 Mountain hemlock 1.03 1.08 1.07 112 e -3 6by f l o t a t i o n i n Water (.998 g cm ), Glucose solutions (1.05 and 1.097), Olive O i l (.918), and Boiled Linseed O i l (.942). APPENDIX 8: Seedling and Water Flow Pathway Dimensions (Treatment Averages) S o i l BD V A needles A roots (kg»m 3) (crn^) (cm) (cm) (cm) (cm^) (cm2) A roots A needles root:shoot r a t i o D o u g l a s - f i r / s i l t y clay 550 138 3075 .060 .0146 108 279 .40 .88 D o u g l a s - f i r / s i l t loam 750 139 2885 .063 .0143 128 263 ,49 .85 Douglas-fir/loamy sand 1120 144 2894 .064 .0146 126 265 ,48 ,88 Western hemlock/ s i l t loam 760 138 3952 .052 .0141 142 350 ,43 ,83 Mountain hemlock/ s i l t loam 760 138 5467 .043 .0136 142 465 31 1.00 APPENDIX 9: Summary of Analysis of Variance of Water Uptake Rate per Unit Root Surface Area -.6 MPA -2.0 MPa S o i l Water Potential Source d.f. S.S. M.S. Source d.f. S.S. M. S. S i l t y Clay X S i l t Loam Treat. Error Total 0.48 1 28 29 ,00032 ,0188 ,0192 ,00032 ,00067 S i l t y Clay X Loamy Sand Treat. Error Total F = 11.06 1 28 29 ,003415 ,00869 ,0121 .003415 ,000308 Treat. Error Total F = 2.49 1 28 29 ,000118 .001327 .001445 ,000118 ,000474 S i l t Loam X Loamy Sand Treat. Error Total F = 2.78 1 28 29 ,0016 ,0161 ,0177 ,0016 .000575 Douglas-fir X Western hemlock Treat. Error Total 14.9 1 28 29 ,00684 ,01284 ,01968 ,00684 ,000459 Treat. Error Total 10.1 1 28 29 .00035 .00097 .00132 ,00035 ,000035 Douglas-fir X Mountain hemlock Western hemlock X Mountain hemlock Treat. Error Total F = 92.3 Treat. Error Total 1 28 29 1 28 29 .040451 .012271 .052722 .00044 .00076 .0012 ,040451 ,000438 ,00044 ,000027 Treat. Error Total F = 21.6 Treat. Error Total 1 28 29 1 28 29 .000716 .00093 .001646 ,0001 .00011 ,00012 .000716 ,0000332 ,0001 ,000004 CO 4> 16.2 F = 2.55 /85 APPENDIX 10: Sample Chamber and S o i l Hygrometer Calibration Information Sample Chambers (using dew-point mode) C-51 slope = 7.99 yV MPa"1 (from -.234 to -4.158 MPa) interpolated intercept — 2.1 yV at 0 MPa measured intercept = 1.7 yV at 0 MPa (using d i s t i l l e d water) max. measured variation * ± .4 yV (at water potentials -.234 to -4.158 MPa) C-52 slope = 7.22 yV MPa"1 (from -.234 to -4.158 MPa) interpolated intercept = 0.2 yV at 0 MPa measured intercept = 0.7 yV at 0 MPa (using d i s t i l l e d water) max. measured va r i a t i o n * ± .3 yV (at water potentials -.234 to -4.158 MPa) The maximum measured variation did not change s i g n i f i c a n t l y for either unit over the water potential range -.234 to -4.158 MPa. S o i l Hygrometers 100 PT51-5 and PT51-10 s o i l hygrometers were purchased i n 1974 and 1976. Of these 100 sensors, 20 were considered unusable by ca l i b r a t i n g at greater than 8.0 yV MPa_i-, cal i b r a t i n g at less than 6.0 yV MPa--'-, demonstrating excessive measurement d r i f t , no readable output or measuring a var i a t i o n of greater than ± .7 yV i n ca l i b r a t i o n osmotic potential solution of -2.241 MPa. Output of .7 yV corresponds to about .1 MPa water potential. A l l hygrometer sensors were calibrated i n osmotic solutions of -2.241 MPa at 20°C and l a t e r i n d i s t i l l e d water using dew-point mode on a Wescor HR-33T dew-point microvoltmeter and a constant temperature (± .02°C) water bath. The following i s a summary of the ca l i b r a t i o n data for the 80 remaining sensors. slope range = 6 to 8 yV MPa ^  mean = 7 yV MPa--'-measured intercept range = 0 to .4 yV (using d i s t i l l e d water) mean = . 2 yV measurement var i a t i o n range = ± .05 to ± .7 yV at -2.241 MPa mean = ± .4 yV The measurement var i a t i o n mean for s o i l hygrometers might be applicable to a wide range of water potentials since sample chamber variation i n dew-point mode did not change over the water potential range of -.234 MPa to -4.158 MPa. Hygrometer Sensor Calibrations for the 80 Remaining Sensors Average h yV output variation yV output # .5m NaCl (±)yv d i s t i l l e d H20 uV bar 1 15.00 .4 .1 .665 4 15.35 .35 .1 .680 7 15.70 .1 .3 .687 8 16.15 .3 .2 .712 9 16.58 .4 .1 .735 11 15.75 .35 .1 .698 12 16.13 .55 .0 .720 13 15.18 .2 .4 .660 14 15.65 .2 .1 .694 15 16.46 .6 .1 .730 16 15.75 .5 .1 .698 18 15.65 .4 .0 .698 19 14.85 .3 .0 .663 21 15.32 .45 .1 .679 22 15.78 .35 .1 .700 24 15.20 .15 .0 .678 26 14.70 .4 .3 .656 27 15.80 .35 .1 .701 28 17.18 .35 .2 .758 29 15.55 .35 .3 .680 30 13.82 .45 .1 .612 31 15.45 .15 .1 .685 32 15.53 .55 .1 .689 33 14.90 .2 .0 .665 34 15.74 .1 .0 .702 35 14.18 .35 .3 .619 37 16.53 .15 .3 .724 38 15.44 .4 .1 .685 40 14.46 .55 .1 .641 41 17.76 .5 .3 .779 -1 Average yV output Variation yV output # .5m NaCl (±)yV d i s t i l l e d H20 yV bar 56 17.96 .35 .2 .793 58 17.80 .4 .1 .790 60 17.28 .4 .3 .758 61 15.78 .15 .2 .695 62 15.45 .35 .1 .685 63 13.66 .55 .1 .605 64 16.70 .25 .3 .732 65 14.48 .35 .2 .637 66 15.78 .3 .0 .704 67 14.99 .4 .1 .664 68 14.04 .65 .3 .613 69 16.73 .35 .2 .738 70 15.90 .35 .2 .701 71 16.78 .4 .1 .744 72 15.48 .35 .3 .677 73 17.20 .35 .4 .750 74 16.15 .45 .1 .716 76 15.24 .2 .1 .676 77 15.16 .25 .2 .668 78 15.93 .5 .1 .706 79 14.83 .25 .1 .657 80 15.50 .6 .2 .683 81 15.52 .45 .0 .693 83 15.06 .4 .0 .672 84 15.28 .45 .1 .677 85 15.86 .2 .0 .708 86 14.64 .05 .2 .644 87 16.35 .2 .1 .726 88 15.54 .2 .1 .690 90 14.84 .2 .1 .658 -1 (cont.) (continued). Average h yV output v a r i a t i o n uV output # .5m NaCl (±)yV d i s t i l l e d R^ O yV bar 43 16.23 .6 .1 .720 44 14.18 .2 .2 .624 45 14.52 .65 .2 .639 47 15.08 .15 .2 .664 48 17.45 .25 .3 .765 50 16.85 .45 .3 .739 51 16.95 .05 .0 .756 52 16.83 .15 .2 .742 53 16.03 .3 .3 .702 54 15.75 .35 .2 .694 -1 (maximum measured value - lowest measured value) 2 Average yV output # .5m NaCl Variation yV output (±)yV d i s t i l l e d H„0 yV bar 91 14.94 .4 .0 .667 92 15.50 .5 .2 .683 93 16.06 .55 .0 .717 94 14.66 .7 .0 .654 95 14.06 .55 .0 .627 96 16.24 .45 .1 .720 97 15.32 .6 .0 .684 98 16.54 .6 .1 .734 99 14.56 .5 .0 .650 100 15.52 .35 .2 .684 variation 

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