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PubMed2003

Changes in gene expression in the wood-forming tissue of transgenic hybrid aspen with increased secondary growth.

Transgenic lines of hybrid aspen with elevated levels of gibberellin (GA) show greatly increased numbers of xylem fibres and increases in xylem fibre length. These plants therefore provide excellent models for studying secondary growth. We have used cDNA microarry analysis to investigate how gene transcription in the developing xylem is affected by GA-induced growth. A recent investigation has shown that genes encoding lignin and cellulose biosynthetic enzymes, as well as a number of transcription factors and other potential regulators of xylogenesis, are under developmental-stage-specific transcriptional control. The present study shows that the highest transcript changes in our transgenic trees occurs in genes generally restricted to the early stages of xylogenesis, including cell division, early expansion and late expansion. The results reveal genes among those arrayed that are up-regulated with an increased xylem production, thus indicating key components in the production of wood.

Cell Wall↗
PubMed1999

Shoot orientation affects vessel size, shoot hydraulic conductivity and shoot growth rate in Vitis vinifera L.

Vitis vinifera L. plants were grown in containers and each plant's single shoot was orientated upwards or downwards. Some plants were trained first upwards, then downwards, then again upwards (N-shaped plants). Vegetative growth was reduced in plants trained downwards compared to that in upward and N-shaped plants. Shoot growth rate slowed in downward shoot portions, but only after the apex had grown downwards for at least 10 internodes. Shoot hydraulic conductivity kh, measured after elimination of xylem embolisms, was lower in downward than in upward plants. In N-shaped plants kh was higher in the upward-growing shoot portions, and lower in the central, downward-growing portion. Shoot- and leaf-specific conductivities were also lower in downward than in upward shoot portions. Xylem cross-sectional area and xylem structure (number of wedges, number of vessels per unit xylem area) differed little in the three orientations. In contrast, vessel diameter and the sum of vessel cross-sectional areas were significantly smaller in downward than in upward shoot portions. These differences could explain the reduction in conductivity observed in the downward-orientated shoot portions. The measurements taken on N-shaped plants showed that the decreases in kh and in vessel size were a result of shoot orientation, not shoot bending.

Biological Transport↗
PubMed2002

A possible stress physiological role of abscisic acid conjugates in root-to-shoot signalling.

Abscisic acid (ABA) conjugates, predominantly their glucose esters, have recently been shown to occur in the xylem sap of different plants. Under stress conditions, their concentration can rise substantially to levels that are higher than the concentration of free ABA. External ABA conjugates cannot penetrate apoplastic barriers in the root. They have to be hydrolysed by apoplastic enzymes in the root cortex. Liberated free ABA can then be redistributed to the root symplast and dragged directly across the endodermis to the stele. Endogenous ABA conjugates are formed in the cytosol of root cells, transported symplastically to the xylem parenchyma cells and released to the xylem vessels. The mechanism of release is unknown; it may include the action of ABC-transporters. Because of its extremely hydrophilic properties, ABA-GE is translocated in the xylem of the stem without any loss to the surrounding parenchyma. After arrival in the leaf apoplast, transporters for ABA-GE in the plasmalemma have to be postulated to redistribute the conjugates to the mesophyll cells. Additionally, apoplastic esterases can cleave the conjugate and release free ABA to the target cells and tissues. The activity of these esterases is increased when barley plants are subjected to salt stress.

Journal Article↗
PubMed1997

Structural cell-wall proteins in protoxylem development: evidence for a repair process mediated by a glycine-rich protein.

Polyclonal antibodies were used to localize structural cell-wall proteins in differentiating protoxylem elements in etiolated bean and soybean hypocotyls at the light- and electron-microscopic level. A proline-rich protein was localized in the lignified secondary walls, but not in the primary walls of protoxylem elements, which remain unlignified, as shown with lignin-specific antibodies. Secretion of the proline-rich protein was observed during lignification in different cell types. A glycine-rich protein (GRP1.8) was specifically localized in the modified primary walls of mature protoxylem elements and in cell corners between xylem elements and xylem parenchyma cells. The protein was secreted by Golgi bodies both in protoxylem cells after the lignification of their secondary walls and in the surrounding xylem parenchyma cells. The modified primary walls of protoxylem elements were visualized under the light microscope as filaments or sheets staining distinctly with the protein stain Coomassie blue. Electron micrographs of these walls show that they are composed of an amorphous material of moderate electron-density and of polysaccharide microfibrils. These materials form a three-dimensional network, interconnecting the ring- or spiral-shaped secondary wall thickenings of protoxylem elements and xylem parenchyma cells. The results demonstrate that the modified primary walls of protoxylem cells are not simply breakdown products due to partial hydrolysis and passive elongation, as believed until now. Extensive repair processes produces cell walls with unique staining properties. It is concluded that these walls are unusually rich in protein and therefore have special chemical and physical properties.

Antibodies↗
PubMed2006

Quorum-sensing regulation governs bacterial adhesion, biofilm development, and host colonization in Pantoea stewartii subspecies stewartii.

The phytopathogenic bacterium Pantoea stewartii subsp. stewartii synthesizes stewartan exo/capsular polysaccharide (EPS) in a cell density-dependent manner governed by the EsaI/EsaR quorum-sensing (QS) system. This study analyzes biofilm development and host colonization of the WT and QS regulatory mutant strains of P. stewartii. First, we show that the cell density-dependent synthesis of stewartan EPS, governed by the EsaI/EsaR QS system, is required for proper bacterial adhesion and development of spatially defined, 3D biofilms. Second, a nonvirulent mutant lacking the esaI gene adheres strongly to surfaces and develops densely packed, less structurally defined biofilms in vitro. This strain appears to be arrested in a low cell density developmental mode. Exposure of this strain to exogenous N-acyl-homoserine lactone counteracts this adhesion phenotype. Third, QS mutants lacking the EsaR repressor attach poorly to surfaces and form amorphous biofilms heavily enmeshed in excess EPS. Fourth, the WT strain disseminates efficiently within the xylem, primarily in a basipetal direction. In contrast, the two QS mutant strains remain largely localized at the site of infection. Fifth, and most significantly, epifluorescence microscopic imaging of infected leaf tissue and excised xylem vessels reveals that the bacteria colonize the xylem with unexpected specificity, particularly toward the annular rings and spiral secondary wall thickenings of protoxylem, as opposed to indiscriminate growth to fill the xylem lumen. These observations are significant to bacterial plant pathogenesis in general and may reveal targets for disease control.

Bacterial Adhesion↗
PubMed1992

Wood contains a cell-wall structural protein.

A pine extensin-like protein (PELP) has been localized in metabolically active cells of differentiating xylem and in mature wood of loblolly pine (Pinus taeda L.). This proline-rich glycosylated protein was purified from cell walls of differentiating xylem by differential solubility and gel electrophoresis. Polyclonal rabbit antibodies were raised against the deglycosylated purified protein (dPELP) and purified antibody was used for immunolocalization. Immunogold and alkaline phosphatase secondary antibody staining both show antigen in secondary cell walls of earlywood and less staining in latewood. Immunoassays of milled dry wood were developed and used to show increased availability of antigen after hydrogen fluoride or cellulase treatment and decreased antigen after chlorite treatment. The specificity of the antigen-antibody reaction was confirmed by competition assays and by preadsorption of antibody to the purified protein. We propose that extensin-like protein is present in xylem cell walls during lignification and that the protein remains as a structural component of cell walls in wood for many years after xylogenesis. We suggest that such structural proteins play important roles in the differentiation of xylem and thereby could affect the properties of wood.

Journal Article↗
PubMed2001

Further observations on the interaction between sugar cane and Gluconacetobacter diazotrophicus under laboratory and greenhouse conditions.

Sugar cane (Saccharum spp.) variety SP 70-1143 was inoculated with Gluconacetobacter diazotrophicus strain PAL5 (ATCC 49037) in two experiments. In experiment 1 the bacteria were inoculated into a modified, low sucrose MS medium within which micropropagated plantlets were rooted. After 10 d there was extensive anatomical evidence of endophytic colonization by G. diazotrophicus, particularly in lower stems, where high numbers of bacteria were visible within some of the xylem vessels. The identity of the bacteria was confirmed by immunogold labelling with an antibody raised against G. diazotrophicus. On the lower stems there were breaks caused by the separation of the plantlets into individuals, and at these 'wounds' bacteria were seen colonizing the xylem and intercellular spaces. Bacteria were also occasionally seen entering leaves via damaged stomata, and subsequently colonizing sub-stomatal cavities and intercellular spaces. A localized host defence response in the form of fibrillar material surrounding the bacteria was associated with both the stem and leaf invasion. In experiment 2, stems of 5-week-old greenhouse-grown plants were inoculated by injection with a suspension of G. diazotrophicus containing 10(8) bacteria ml(-1). No hypersensitive response (HR) was observed, and no symptoms were visible on the leaves and stems for the duration of the experiment (7 d). Close to the point of inoculation, G. diazotrophicus cells were observed within the protoxylem and the xylem parenchyma, where they were surrounded by fibrillar material that stained light-green with toluidine blue. In leaf samples taken up to 4 cm from the inoculation points, G. diazotrophicus cells were mainly found within the metaxylem, where they were surrounded by a light green-staining material. The bacteria were growing in relatively low numbers adjacent to the xylem cell walls, and they were separated from the host-derived material by electron-transparent 'haloes' that contained material that reacted with the G. diazotrophicus antibody.

Acetobacteraceae↗
PubMed2002

Cavitation fatigue and its reversal in sunflower (Helianthus annuus L.).

"Cavitation fatigue" is the increased susceptibility of a xylem conduit to cavitation as a result of its prior cavitation. It was investigated whether cavitation fatigue induced in vivo could be repaired in intact plants. Sunflowers (Helianthus annuus L.) were subjected to soil drought in the greenhouse. Native embolism and vulnerability to cavitation was measured in well-watered controls and after 5 d and 10 d of controlled drought. A dramatic cavitation fatigue was observed where droughted xylem that was refilled in the laboratory developed up to 60 PLC (percentage loss of hydraulic conductivity) at -1 MPa versus only 5.2 PLC in non-droughted controls. Rewatered plants showed the complete reversal of cavitation fatigue over 4 d. Reversal of fatigue was correlated with the refilling of embolized vessels in the intact plants (r(2)=0.91, P<0.01), suggesting that xylem transport to fatigued vessels was required for their repair. The in vivo reversal of fatigue was partially duplicated in excised stem segments by perfusing them with root exudates from droughted (DR) and well-watered (WW) plants. The DR exudate had a greater effect, and this was associated with a greater pH in the DR versus WW saps, but there was no difference in total cation concentration. Perfusions with 2 mM CaCl(2) and KCl solutions also partially reversed cavitation fatigue as opposed to no effect with deionized water, suggesting a role of ions in addition to a pH effect. It is suspected that fatigue is caused by stretching and partial disruption of linkages between cellulose microfibrils in inter-conduit pit membranes during air seeding, and that the reversal of fatigue involves restoring these linkages by ingredients in xylem sap.

Biological Transport↗
PubMed2003

Root pressurization affects growth-induced water potentials and growth in dehydrated maize leaves.

Profiles of water potential (Psi w) were measured from the soil to the tips of growing leaves of maize (Zea mays L.) when pressure (P) was applied to the soil/root system. At moderately low soil Psi w, leaf elongation was somewhat inhibited, large tensions existed in the xylem, and Psi w were slightly lower in the elongating leaf tissues than in the xylem, i.e. a growth-induced Psi w was present but small. With P, the tension was relieved, enlarging the difference in Psi w between the xylem and the elongating tissues, i.e. enlarging the growth-induced Psi w, which is critical for growth. Guttation occurred, confirming the high Psi w of the xylem, and the mature leaf tissue rehydrated. Water uptake increased and met the requirements of transpiration. Leaf elongation recovered to control rates. Under more severe conditions at lower soil Psi w, P induced only a brief elongation and the growth-induced Psi w responded only slightly. Guttation did not occur, water flow did not meet the requirements of transpiration, and the mature leaf tissues did not rehydrate. A rewatering experiment indicated that a low conductance existed in the severely dehydrated soil, which limited water delivery to the root and shoot. Therefore, the initial growth inhibition appeared to be hydraulic because the enlargement of the growth-induced Psi w by P together with rehydration of the mature leaf tissue were essential for growth recovery. In more severe conditions, P was ineffective because the soil could not supply water at the required rate, and metabolic factors began to contribute to the inhibition.

Biological Transport↗
PubMed1992

Vulnerability of several conifers to air embolism.

Hydraulic properties of xylem in seven species of conifer were studied during late winter and early spring 1991. Vulnerability to cavitation and air embolism was investigated using hydraulic conductivity and acoustic techniques. Embolisms were induced in branches excised from mature trees by air-drying them in the laboratory. Both techniques gave comparable results indicating that they both assess the same phenomenon. Within a tree, vulnerability was related to the permeability of the xylem, the largest stems tended to cavitate before the smallest ones when water deficits developed in a branch. Interspecific comparisons showed large differences in the xylem water potential needed to induce significant embolism, values ranged from -2.5 MPa in Pinus sylvestris to -4 MPa in Cedrus atlantica, but these differences did not correlate with differences in the xylem permeability of the species. The vulnerability of a species to air embolism was found to be consistent with its ecophysiological behavior in the presence of water stress, drought-tolerant species being less vulnerable than drought-avoiding species.

Journal Article↗
PubMed1993

Variation in seedling hydraulic architecture as a function of species and environment.

Northern red oak (Quercus rubra L.) and yellow-poplar (Liriodendron tulipifera L.) were grown for two years in full sunlight (unshaded) or 20% of full sunlight (shaded) under either well-watered or drought conditions. There was a close association between evaporative flux (in situ) and leaf-specific conductivity (LSC) in stem segments of both species. Shaded, drought-stressed seedlings of both species had significantly reduced leaf area, evaporative flux, volume flow rate in xylem, flow velocity, potentially functional xylem area, and LSC than unshaded, well-watered seedlings. Reductions in LSC associated with drought or shade were similar for both species; and within a treatment, both species had similar LSC. Species differed in the manner of LSC adjustment to drought and shade. Reductions in leaf area associated with drought or shade were accompanied primarily by reductions in potentially functional xylem area for L. tulipifera, and by reductions in flow velocity for Q. rubra. These results suggest (1) the existence of a homeostatic balance between evaporative flux and LSC, (2) that species with widely different growth patterns and xylem anatomies may develop similar LSC within the same environment, and (3) a possible hydraulic basis for differences in habitat between ring- and diffuse-porous species.

Journal Article↗
PubMed1997

Control of longitudinal and cambial growth by gibberellins and indole-3-acetic acid in current-year shoots of Pinus sylvestris.

We investigated the involvement of gibberellins (GAs) and indole-3-acetic acid (IAA) in the control of longitudinal and cambial growth in current-year shoots of Pinus sylvestris L. Elongating terminal shoots, located at the apex of previous-year (1-year-old) branches in the uppermost whorl on the main stem, were variously decapitated (apical 5 to 10 mm removed), defoliated (all developing needle fascicles removed) and treated with endogenous GA(4/7) or IAA, or both. Shoot length and the radial widths of xylem and phloem were measured, and the concentrations of GA(1), GA(3), GA(4), GA(9) and IAA in the stem were determined by combined gas chromatography-mass spectrometry with deuterated GAs and [(13)C(6)]-IAA as internal standards. Decapitation decreased the production of xylem and phloem and the IAA concentration, but did not alter either longitudinal growth or the concentrations of GAs. Defoliation markedly inhibited shoot elongation, as well as cambial growth, and reduced the concentrations of GA(1), GA(3), GA(4), GA(9) and IAA. Application of GA(4/7) to defoliated shoots promoted longitudinal growth and phloem production, without affecting xylem production or IAA concentration. Application of GA(4/7) and IAA together to decapitated + defoliated shoots increased shoot elongation, xylem and phloem production and IAA concentration, whereas applying either substance alone had a smaller effect or none at all. We conclude that, for elongating current-year shoots of Pinus sylvestris, (1) both the shoot apex and the developing needle fascicles are major sources of the IAA present in the stem, whereas stem GAs originate primarily in the needle fascicles, (2) GAs and IAA are required for both shoot elongation and cambial growth, and (3) GAs act directly in the control of shoot growth, rather than indirectly through affecting the IAA concentration.

Journal Article↗
PubMed1999

Sap-flux-scaled transpiration responses to light, vapor pressure deficit, and leaf area reduction in a flooded Taxodium distichum forest.

We used 20-mm-long, Granier-type sensors to quantify the effects of tree size, azimuth and radial position in the xylem on the spatial variability in xylem sap flux in 64-year-old trees of Taxodium distichum L. Rich. growing in a flooded forest. This information was used to scale flux to the stand level to investigate variations in half-hourly and daily (24-hour) sums of sap flow, transpiration per unit of leaf area, and stand transpiration in relation to vapor pressure deficit (D) and photosynthetically active radiation (Q(o)). Measurements of xylem sap flux density (J(s)) indicated that: (1) J(s) in small diameter trees was 0.70 of that in medium and large diameter trees, but the relationship between stem diameter as a continuous variable and J(s) was not significant; (2) J(s) at 20-40 mm depth in the xylem was 0.40 of that at 0-20 mm depth; and (3) J(s) on the north side of trees was 0.64 of that in directions 120 degrees from the north. Daily transpiration was linearly related to daily daytime mean D, and reached a modest value of 1.3 mm day(-1), reflecting the low leaf area index (LAI = 2.2) of the stand. Because there was no soil water limitation, half-hourly water uptake was nearly linearly related to D at D < 0.6 kPa during both night and day, increasing to saturation during daytime at higher values of D. The positive effect of Q(o) on J(s) was significant, but relatively minor. Thus, a second-order polynomial with D explained 94% of the variation in J(s) and transpiration. An approximately 40% reduction in LAI by a hurricane resulted in decreases of about 18% in J(s) and stand transpiration, indicating partial stomatal compensation.

Journal Article↗
PubMed2002

Radial patterns of sap flow in woody stems of dominant and understory species: scaling errors associated with positioning of sensors.

We studied sap flow in dominant coniferous (Pinus sylvestris L.) and broadleaf (Populus canescens L.) species and in understory species (Prunus serotina Ehrh. and Rhododendron ponticum L.) by the heat field deformation (HFD) method. We attempted to identify possible errors arising during flow integration and scaling from single-point measurements to whole trees. Large systematic errors of -90 to 300% were found when it was assumed that sap flow was uniform over the sapwood depth. Therefore, we recommend that the radial sap flow pattern should be determined first using sensors with multiple measuring points along a stem radius followed by single-point measurements with sensors placed at a predetermined depth. Other significant errors occurred in the scaling procedure even when the sap flow radial pattern was known. These included errors associated with uncertainties in the positioning of sensors beneath the cambium (up to 15% per 1 mm error in estimated xylem depth), and differences in environmental conditions when the radial profile applied for integration was determined over the short term (up to 47% error). High temporal variation in the point-to-area correction factor along the xylem radius used for flow integration is also problematic. Compared with midday measurements, measurements of radial variation of sap flow in the morning and evening of sunny days minimized the influence of temporal variations on the point-to-area correction factor, which was especially pronounced in trees with a highly asymmetric sap flow radial pattern because of differences in functioning of the sapwood xylem layers. Positioning a single-point sensor at a depth with maximum sap flow is advantageous because of the high sensitivity of maximum sap flow to water stress conditions and changes in micro-climate, and because of the lower random errors associated with the positioning of a single-point sensor along the xylem radius.

Pinus↗
PubMed2003

Temporal water deficit and wood formation in Cryptomeria japonica.

Cell behavior in the cambium and developing xylem of 3-year-old Japanese cedar (Cryptomeria japonica D. Don.) trees, during and after an 11-day suspension of irrigation, was analyzed. Leaf xylem pressure potential and tangential strain of the stem surface were monitored throughout the experiment. Anatomical features and numbers of developing tracheids and cambial cells were observed in four trees, sampled on Days 0, 4, 8 and 11 after irrigation was suspended. Daytime xylem pressure potential decreased to -1.9 MPa on Day 7 and remained the same until irrigation was resumed on Day 11. The transverse dimensions of the tracheids, which began to form secondary walls, began to decrease on Day 4. The number of cells in the cambial zone and cell expansion zone decreased abruptly on Day 8. Tangentially aligned developing tracheids with collapsed cell walls were observed in samples harvested on Days 8 and 11. Secondary wall formation was recognized in these tracheids. After the resumption of irrigation, xylem pressure potential recovered rapidly to the same value as before the suspension of irrigation. Tangential strain increased within 30 min after the resumption of irrigation, and continued to increase until the onset of light the next day. Eighteen days after the resumption of irrigation, anatomical features of cells in the cambium and cell-expansion zone were similar to those observed before suspension of irrigation.

Cryptomeria↗
PubMed2003

Reliance on stored water increases with tree size in three species in the Pacific Northwest.

In tall old forests, limitations to water transport may limit maximum tree height and reduce photosynthesis and carbon sequestration. We evaluated the degree to which tall trees could potentially compensate for hydraulic limitations to water transport by increased use of water stored in xylem. Using sap flux measurements in three tree species of the Pacific Northwest, we showed that reliance on stored water increases with tree size and estimated that use of stored water increases photosynthesis. For Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), water stored in xylem accounted for 20 to 25% of total daily water use in 60-m trees, whereas stored water comprised 7% of daily water use in 15-m trees. For Oregon white oak (Quercus garryana Dougl. ex Hook.), water stored in xylem accounted for 10 to 23% of total daily water use in 25-m trees, whereas stored water comprised 9 to 13% of daily water use in 10-m trees. For ponderosa pine (Pinus ponderosa Dougl. ex Laws.), water stored in xylem accounted for 4 to 20% of total daily water use in 36-m trees, whereas stored water comprised 2 to 4% of daily water use in 12-m trees. In 60-m Douglas-fir trees, we estimated that use of stored water supported 18% more photosynthesis on a daily basis than would occur if no stored water were used, whereas 15-m Douglas-fir trees gained 10% greater daily photosynthesis from use of stored water. We conclude that water storage plays a significant role in the water and carbon economy of tall trees and old forests.

Northwestern United States↗
PubMed2004

Assessing variation in the radial profile of sap flux density in Pinus species and its effect on daily water use.

We monitored sap flux density (v) diurnally in nine mature southeastern pine (Pinus spp.) trees with a thermal dissipation probe that spanned the sapwood radius. We found the expected pattern of high v near the cambium and decreasing v with depth toward the center of the tree; however, the pattern was not constant within a day or between trees. Radial profiles of trees were steeper earlier in the day and became less steep later in the day. As a result, time-dependent changes in the shape of the radial profile of v were sometimes correlated with daily changes in evaporative demand. As the radial profile became less steep, the inner xylem contributed relatively more to total tree sap flow than it did earlier in the day. We present a 3-parameter Gaussian function that can be used to describe the radial distribution of v in trees. Parameters in the function represent depth in the xylem from the cambium, maximum v, depth in the xylem where maximum v occurs, and the rate of radial change in v with radial depth (beta). Values of beta varied significantly between trees and with time, and were sometimes correlated with air vapor pressure deficit (D). We hypothesize that this occurred during periods of high transpiration when the water potential gradient became great enough to move water in the inner sapwood despite its probable high hydraulic resistance. We examined discrepancies among estimates of daily water use based on single-point, two-point and multi-point (i.e., every 20 mm in the sapwood) measurements. When radial distribution of v was not considered, a single-point measurement resulted in errors as large as 154% in the estimate of daily water use relative to the estimate obtained from a multi-point measurement. Measuring v at two close sample points (10 and 30 mm) did not improve the estimate; however, estimates derived from v measured at two distant sample points (10 and 70 mm) significantly improved the estimate of daily water use, although errors were as great as 32% in individual trees. The variability in v with depth in the xylem, over time, and between trees indicates that measurements of the radial distribution of v are necessary to accurately estimate water flow in trees with large sapwood areas.

Circadian Rhythm↗
PubMed1988

Planting stress in newly planted jack pine and white spruce. 2. Changes in tissue water potential components.

Water relations of bare-root jack pine (Pinus banksiana Lamb.) and white spruce (Picea glauca (Moench) Voss) planted in a greenhouse and on a boreal cut-over site were examined during the first growing season. In field-planted trees, maximum stomatal conductances (g(wv)) were initially low (< 0.10 cm s(-1)). Base and minimum xylem pressure potentials (Psi(x(base)) and Psi(x(min))) were less than -1.5 and -1.7 MPa for jack pine and -2.0 and -2.6 MPa for white spruce, respectively. During the growing season, maximum g(wv) increased in both species to around 0.2 cm s(-1). Base and minimum xylem pressure potentials also increased in both species to around -0.5 and -1.0 MPa in jack pine and -1.0 and -1.5 MPa in white spruce, respectively. Minimum xylem pressure potentials in white spruce fell below the turgor loss point during the first half of the growing season. Osmotic potential at the turgor loss point Psi(pi(TLP)) decreased after field planting to around -2.7 and -2.3 MPa in jack pine and white spruce, respectively. In the greenhouse, minimum values of Psi(pi(TLP)) were -2.2 and -2.3 MPa in jack pine and white spruce, respectively. Maximum bulk modulus of elasticity was greater in white spruce and underwent greater seasonal change than in jack pine. Relative water content (RWC) at turgor loss ranged between 71 and 74% in jack pine and 80 and 87% in white spruce. Available turgor (T(avail)), defined as the integral of turgor over the range of RWC between Psi(x(base)) and xylem pressure potential at the turgor loss point, was similar in jack pine and white spruce just after field planting. For the rest of the growing season, however, T(avail) in jack pine was two to three times that in white spruce. Diurnal turgor (T(diurnal)), defined as the integral of turgor over the range of RWC between Psi(x(base)) and Psi(x(min)), as a percent of T(avail) was higher in field-planted white spruce than jack pine until the end of the season. Dynamics of tissue water potential components are discussed in relation to plantation establishment.

Journal Article↗