{"http:\/\/dx.doi.org\/10.14288\/1.0094389":{"http:\/\/vivoweb.org\/ontology\/core#departmentOrSchool":[{"value":"Forestry, Faculty of","type":"literal","lang":"en"}],"http:\/\/www.europeana.eu\/schemas\/edm\/dataProvider":[{"value":"DSpace","type":"literal","lang":"en"}],"https:\/\/open.library.ubc.ca\/terms#degreeCampus":[{"value":"UBCV","type":"literal","lang":"en"}],"http:\/\/purl.org\/dc\/terms\/creator":[{"value":"Dosskey, Michael Gordon","type":"literal","lang":"en"}],"http:\/\/purl.org\/dc\/terms\/issued":[{"value":"2010-02-26T01:09:41Z","type":"literal","lang":"en"},{"value":"1978","type":"literal","lang":"en"}],"http:\/\/vivoweb.org\/ontology\/core#relatedDegree":[{"value":"Master of Science - MSc","type":"literal","lang":"en"}],"https:\/\/open.library.ubc.ca\/terms#degreeGrantor":[{"value":"University of British Columbia","type":"literal","lang":"en"}],"http:\/\/purl.org\/dc\/terms\/description":[{"value":"Water availability for uptake by tree seedlings is determined both by the soil water potential in relation to seedling needle water potential and by the resistance to flow of water through the soil, root and stem, to the needles. This study was designed to focus principally on water uptake resistances. The effects of soil 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 soil-plant system.\r\nThe study was conducted on one-year-old potted seedlings in a controlled environment growth chamber.\r\nNeedle water potential (\u03a8N) of Douglas-fir is not much affected by soil water potential (\u03a8s) down to about -2.5 MPa, where the calculated water uptake rate becomes very small. However, soil texture does significantly affect the resistance to flow into the seedling and thus affects the water uptake rate by the seedling. The total resistance to water uptake increases as the soil dries. Coarser textured soils show consistently higher water uptake resistances over the soil water potential range -0.5 to -2.5 MPa. It is inferred that differences in resistance are associated with unsaturated, hydraulic conductivity characteristics of the soil and soil-root contact.\r\nUnlike Douglas-fir, both western and mountain hemlock show a large decrease in needle water potential as the soil dries down to\r\n\r\na \u03a8s of about -3.0 MPa. The water potential difference (\u03a8s - \u03a8N) for\r\nhemlocks is less where \u03a8s is higher than -1.8 MPa, and greater where\r\n\u03a8s is less than -1.8 MPa, than (\u03a8s - \u03a8N ) for Douglas-fir in these s s N\r\nexperiments. Despite these differences, the resistance to water uptake for both hemlock species is much greater over the soil 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 soil, even though root densities and root surface areas are much larger for the hemlocks. This behavior is most pronounced with mountain hemlock. These differences are thought to be related to higher tissue and (perhaps) soil-root contact resistances in the hemlock species. The soil resistance appears to be small, at least down to \u03a8s of about -2.0 MPa, in these experiments. However, root densities are probably much greater than one might expect in the field.","type":"literal","lang":"en"}],"http:\/\/www.europeana.eu\/schemas\/edm\/aggregatedCHO":[{"value":"https:\/\/circle.library.ubc.ca\/rest\/handle\/2429\/20998?expand=metadata","type":"literal","lang":"en"}],"http:\/\/www.w3.org\/2009\/08\/skos-reference\/skos.html#note":[{"value":"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 \u00a3>c~f. 6 . \/97<\u00a3 \/ 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 (
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\u2022g-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\u00b0C) 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^\u2014)^ (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 \u2014 ( 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 \/ \u2022 . \u2014* 1 cr a. a i w \u00bb* 5 = r-\/ \/ \/ \/ \/ \/ \/ \/ .mLU ' I\u2014 O Q_ Ct LU o l \u2014 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\u2014 ED Q_ CC UJ Oh-i ^ UJ a U J . in i .(\u00a3> 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 ' \u00b0 i i (X a. in 2= I ex .roLU \u2022 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 ~ *\u2014 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 \u2014 a \u2014 r-\u2014 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\u2014( I cr Q_ cr cr i\u2014i . r\\juJ ' (\u2014 \u00a3D Q_ cr LU in I\u2014 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; \u2022 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 \u2022 r-\u2022 in |-cn CD LO CL - ^ L U :\u00b0<-> \u2022 -z. - r-tr - t \u2014 - to LU -roCe: LU - ^ cn \u2014I 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. These characteristics are controlled both by the a b i l i t y to control water potential difference through needle water potential and by the resistance to water flow to the absorbing root surface, into the root and through the xylem to the needles. Thus s o i l water potential alone may be an i n s u f f i c i e n t indicator of water a v a i l a b i l i t y to tree seedlings. no REFERENCES Andrews, R. E. and E. I. Newman. 1969. Resistance to water flow i n s o i l and plant. I I I . Evidence from experiments with wheat. New Phytol. 68 : 1051-8. Ballard, T. M., T. A. Black and K. G. McNaughton. 1977. Summer energy balance and temperatures i n a forest clearcut i n southwestern B r i t i s h Columbia. In: Energy, water and the physical environment of the s o i l . 6th B.C. S o i l Science Workshop Report, Richmond, B.C. pp. 74-86. Boyer, J. S. 1967. Leaf water potential measured with a pressure chamber. Plant Physiol. 42: 133-137. Boyer, J. S. 1969. Free-energy transfer i n plants. 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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\u201e0 (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,\u20227H\u201e0 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\u00b0 50' 123 48' 92B13\/B2\/315\/1.5 Western hemlock Latitude Longitude B.C.F.S. Seed Lot Ident. No. 49\u00b0 40' 123 50' 92H11\/B3\/2476\/112B Mountain hemlock Latitude Longitude B.C.F.S. Seed Lot Ident. No. 49\u00b0 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\/\"-\"\u00a3w ) 1N31N0D 83\u00b1V\/*\\ 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\u00bbm 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 \u2014 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 * \u00b1 .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 * \u00b1 .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 \u00b1 .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\u00b0C 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 (\u00b1 .02\u00b0C) 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 = \u00b1 .05 to \u00b1 .7 yV at -2.241 MPa mean = \u00b1 .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 (\u00b1)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 (\u00b1)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 (\u00b1)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 (\u00b1)yV d i s t i l l e d H\u201e0 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 ","type":"literal","lang":"en"}],"http:\/\/www.europeana.eu\/schemas\/edm\/hasType":[{"value":"Thesis\/Dissertation","type":"literal","lang":"en"}],"http:\/\/www.europeana.eu\/schemas\/edm\/isShownAt":[{"value":"10.14288\/1.0094389","type":"literal","lang":"en"}],"http:\/\/purl.org\/dc\/terms\/language":[{"value":"eng","type":"literal","lang":"en"}],"https:\/\/open.library.ubc.ca\/terms#degreeDiscipline":[{"value":"Forestry","type":"literal","lang":"en"}],"http:\/\/www.europeana.eu\/schemas\/edm\/provider":[{"value":"Vancouver : University of British Columbia Library","type":"literal","lang":"en"}],"http:\/\/purl.org\/dc\/terms\/publisher":[{"value":"University of British Columbia","type":"literal","lang":"en"}],"http:\/\/purl.org\/dc\/terms\/rights":[{"value":"For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https:\/\/open.library.ubc.ca\/terms_of_use.","type":"literal","lang":"en"}],"https:\/\/open.library.ubc.ca\/terms#scholarLevel":[{"value":"Graduate","type":"literal","lang":"en"}],"http:\/\/purl.org\/dc\/terms\/title":[{"value":"Resistance to water uptake by conifer seedlings","type":"literal","lang":"en"}],"http:\/\/purl.org\/dc\/terms\/type":[{"value":"Text","type":"literal","lang":"en"}],"https:\/\/open.library.ubc.ca\/terms#identifierURI":[{"value":"http:\/\/hdl.handle.net\/2429\/20998","type":"literal","lang":"en"}]}}