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  • 1
    Electronic Resource
    Electronic Resource
    Control of transpiration in three coffee cultivars: the role of hydraulic and crown architecture (2000)
    Springer
    Trees 14 (2000), S. 181-190 
    Details
    ISSN: 0931-1890
    Keywords: Key words  Coffee arabica ; Hydraulic conductance ; Sap flow ; Stomata ; Stomatal decoupling coefficient
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  Water use and hydraulic architecture were studied in the coffee (Coffea arabica) cultivars San Ramon, Yellow Caturra and Typica growing in the field under similar environmental conditions. The cultivars differed in growth habit, crown architecture, basal sapwood area and total leaf surface area. Transpiration per unit leaf area (E), stomatal conductance (g s), crown conductance (g c), total hydraulic conductance of the soil/leaf pathway (G t) and the stomatal decoupling coefficient, omega (Ω) (Jarvis and McNaughton 1986) were assessed over a range of soil moisture and during partial defoliation treatments. The relationship between sap flow and sapwood area was linear and appeared to be similar for the three cultivars. Variation in g c, E, and G t of intact plants and leaf area-specific hydraulic conductivity (k l) of excised lateral branches was negatively correlated with variation in the ratio of leaf area to sapwood area. Transpiration, g c, and g s were positively correlated with G t. Transpiration and G t varied with total leaf area and were greatest at intermediate values (10 m2) of leaf area. Omega was greatest in Yellow Caturra, the cultivar with the greatest leaf area and a dense crown, and was smallest in Typica, the cultivar with an open crown. Differences in omega were attributable primarily to differences in leaf boundary layer conductance among the cultivars. Plants of each cultivar that were 40% defoliated maintained sap flows comparable to pretreatment plants, but expected compensatory increases in g s were not consistently observed. Despite their contrasting crown morphologies and hydraulic architecture, the three cultivars shared common relationships between water use and hydraulic architectural traits.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00009762
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  • 2
    Electronic Resource
    Electronic Resource
    Does turgor limit growth in tall trees? (2004)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 27 (2004), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The gravitational component of water potential contributes a standing 0.01 MPa m−1 to the xylem tension gradient in plants. In tall trees, this contribution can significantly reduce the water potential near the tree tops. The turgor of cells in buds and leaves is expected to decrease in direct proportion with leaf water potential along a height gradient unless osmotic adjustment occurs. The pressure–volume technique was used to characterize height-dependent variation in leaf tissue water relations and shoot growth characteristics in young and old Douglas-fir trees to determine the extent to which growth limitation with increasing height may be linked to the influence of the gravitational water potential gradient on leaf turgor. Values of leaf water potential (Ψl), bulk osmotic potential at full and zero turgor, and other key tissue water relations characteristics were estimated on foliage obtained at 13.5 m near the tops of young (approximately 25-year-old) trees and at 34.7, 44.2 and 55.6 m in the crowns of old-growth (approximately 450-year-old) trees during portions of three consecutive growing seasons. The sampling periods coincided with bud swelling, expansion and maturation of new foliage. Vertical gradients of Ψl and pressure–volume analyses indicated that turgor decreased with increasing height, particularly during the late spring when vegetative buds began to swell. Vertical trends in branch elongation, leaf dimensions and leaf mass per area were consistent with increasing turgor limitation on shoot growth with increasing height. During the late spring (May), no osmotic adjustment to compensate for the gravitational gradient of Ψl was observed. By July, osmotic adjustment had occurred, but it was not sufficient to fully compensate for the vertical gradient of Ψl. In tall trees, the gravitational component of Ψl is superimposed on phenologically driven changes in leaf water relations characteristics, imposing potential constraints on turgor that may be indistinguishable from those associated with soil water deficits.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.2003.01141.x
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  • 3
    Electronic Resource
    Electronic Resource
    Hydraulic architecture of sugarcane in relation to patterns of water use during plant development (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 15 (1992), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Hydraulic conductance was measured on leaf and stem segments excised from sugarcane plants at different stages of development. Maximum transpiration rates and leaf water potential (ΨL) associated with maximum transpiration were also measured in intact plants as a function of plant size. Leaf specific hydraulic conductivity (Lsc) and transpiration on a unit leaf area basis (E) were maximal in plants with approximately 0.2 m2 leaf area and decreased with increasing plant size. These changes in Fand Lsc were nearly parallel, which prevented φL in larger plants from decreasing to levels associated with substantial loss in xylem conductivity caused by embolism formation. Coordination of changes in E and leaf hydraulic properties was not mediated by declining leaf water status, since φL increased with plant size. Hydraulic constrictions were present at nodes and in the node-leaf sheath-leaf blade pathway. This pattern of constrictions is in accord with the idea of plant segmentation into regions differing in water transport efficiency and would tend to confine embolisms to the relatively expendable leaves at terminal positions in the pathway, thereby preserving water transport through the stem.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1992.tb00998.x
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  • 4
    Electronic Resource
    Electronic Resource
    Whole-tree water transport scales with sapwood capacitance in tropical forest canopy trees (2003)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 26 (2003), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The present study examines the manner in which several whole-tree water transport properties scale with species-specific variation in sapwood water storage capacity. The hypothesis that constraints on relationships between sapwood capacitance and other water relations characteristics lead to predictable scaling relationships between intrinsic capacitance and whole-tree behaviour was investigated. Samples of sapwood from four tropical forest canopy tree species selected to represent a range of wood density, tree size and architecture, and taxonomic diversity were used to generate moisture release curves in thermocouple psychrometer chambers, from which species-specific values of sapwood capacitance were calculated. Sapwood capacitance was then used to scale several whole-tree water transport properties determined from measurements of upper branch and basal sap flow, branch water potential, and axial and radial movement of deuterated water (D2O) injected into the base of the trunk as a tracer. Sapwood capacitance ranged from 83 to 416 kg m−3 MPa−1 among the four species studied and was strongly correlated with minimum branch water potential, soil-to-branch hydraulic conductance, daily utilization of stored water, and axial and radial movement of D2O. The species-independent scaling of several whole-tree water transport properties with sapwood capacitance indicated that substantial convergence in plant function at multiple levels of biological organization was revealed by a simple variable related to a biophysical property of water transport tissue.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.2003.01039.x
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  • 5
    Electronic Resource
    Electronic Resource
    Dynamic changes in hydraulic conductivity in petioles of two savanna tree species: factors and mechanisms contributing to the refilling of embolized vessels (2003)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 26 (2003), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Diel variation in specific hydraulic conductivity (ks) was recorded in petioles of two savanna tree species, Schefflera macrocarpa and Caryocar brasiliense, from central Brazil. These two species have compound leaves with long petioles (10–30 cm). In both species, petiole ks decreased sharply with increasing transpiration rates and declining leaf water potentials (ψL) during the morning. Petiole ks increased during the afternoon while the plants were still transpiring and the water in the non-embolized vessels was still under tension. Dye experiments confirmed that in both species diel variation in ks was associated with embolism formation and repair. When transpiration was prevented in individual leaves, their petiole ks and water potential remained close to their maximum values during the day. When minimum daily ψL on selected branches was experimentally lowered by 0.2–0.6 MPa, the rate of ks recovery during the afternoon was slower in comparison with control branches. Several field manipulations were performed to identify potential mechanisms involved in the refilling of embolized petiole vessels. Removal of the cortex or longitudinal incisions in the cortex prevented afternoon recovery of ks and refilling of embolized vessels. When distilled water was added to petiole surfaces that had been abraded to partially remove the cuticle, ks increased sharply during the morning and early afternoon. Evidence of starch to sugar conversion in the starch sheath cells surrounding the vascular bundles of the petioles was observed during periods of rapid transpiration when the abundance of starch granules in the starch sheath cells surrounding the vascular bundles decreased. Consistent with this, petiole sugar content was highest in the early afternoon. The most parsimonious explanation of the field observations and the experimental results was that an increase in osmotically active solutes in cells outside the vascular bundles at around midday leads to water uptake by these cells. However, the concurrent increase in tissue volume is partially constrained by the cortex, resulting in a transient pressure imbalance that may drive radial water movement in the direction of the embolized vessels, thereby refilling them and restoring water flow. This study thus presents evidence that embolism formation and repair are two distinct phenomena controlled by different variables. The degree of embolism is a function of tension, and the rate of refilling a function of internal pressure imbalances.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.0140-7791.2003.01082.x
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  • 6
    Electronic Resource
    Electronic Resource
    Stem water storage and diurnal patterns of water use in tropical forest canopy trees (1998)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 21 (1998), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Stem water storage capacity and diurnal patterns of water use were studied in five canopy trees of a seasonal tropical forest in Panama. Sap flow was measured simultaneously at the top and at the base of each tree using constant energy input thermal probes inserted in the sapwood. The daily stem storage capacity was calculated by comparing the diurnal patterns of basal and crown sap flow. The amount of water withdrawn from storage and subsequently replaced daily ranged from 4 kg d–1 in a 0·20-m-diameter individual of Cecropia longipes to 54 kg d–1 in a 1·02-m-diameter individual of Anacardium excelsum, representing 9–15% of the total daily water loss, respectively. Ficus insipida, Luehea seemannii and Spondias mombin had intermediate diurnal water storage capacities. Trees with greater storage capacity maintained maximum rates of transpiration for a substantially longer fraction of the day than trees with smaller water storage capacity. All five trees conformed to a common linear relationship between diurnal storage capacity and basal sapwood area, suggesting that this relationship was species-independent and size-specific for trees at the study site. According to this relationship there was an increment of 10 kg of diurnal water storage capacity for every 0·1 m2 increase in basal sapwood area. The diurnal withdrawal of water from, and refill of, internal stores was a dynamic process, tightly coupled to fluctuations in environmental conditions. The variations in basal and crown sap flow were more synchronized after 1100 h when internal reserves were mostly depleted. Stem water storage may partially compensate for increases in axial hydraulic resistance with tree size and thus play an important role in regulating the water status of leaves exposed to the large diurnal variations in evaporative demand that occur in the upper canopy of seasonal lowland tropical forests.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.1998.00273.x
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  • 7
    Electronic Resource
    Electronic Resource
    Turgor and osmotic relations of the desert shrub Larrea tridentata (1986)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 9 (1986), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Leaf water relations characteristics of creosote bush, Larrea tridentata, were studied in view of previous reports that its leaves commonly experience zero or negative turgor under dry conditions. Leaf turgor loss point (〈inlineGraphic alt="inline image" href="urn:x-wiley:01407791:PCE467:PCE_467_mu1" location="equation/PCE_467_mu1.gif"/〉) was determined by a pressure-volume method for samples subjected to a hydration procedure and for untreated samples. Hydration caused 〈inlineGraphic alt="inline image" href="urn:x-wiley:01407791:PCE467:PCE_467_mu1" location="equation/PCE_467_mu1.gif"/〉 to increase by as much as 3 M Pa. Hydration of samples also caused changes in other leaf water relations characteristics such as symplastic solute content, tissue elasticity and symplasmic water fraction, but total leaf solute content was unchanged. Comparison of our field plant water potential data with values of 〈inlineGraphic alt="inline image" href="urn:x-wiley:01407791:PCE467:PCE_467_mu1" location="equation/PCE_467_mu1.gif"/〉 obtained by the two methods resulted in predictions of turgor loss during part or all of a diurnal cycle based on hydrated samples, and turgor maintenance (at least 0.3 MPa) based on untreated samples. Pooled data for 〈inlineGraphic alt="inline image" href="urn:x-wiley:01407791:PCE467:PCE_467_mu1" location="equation/PCE_467_mu1.gif"/〉 obtained from both partially hydrated and untreated samples showed that L. tridentata maintains fairly constant levels of turgor over a wide range of leaf water potential. Dilution of cell contents by apoplastic water introduced significant errors in psychrometric determinations of osmotic potential in both frozen and thawed leaf tissue and expressed cell sap. Use of these values of osmotic potential resulted in predictions of zero turgor at all plant water potentials measured in the field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1986.tb01762.x
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  • 8
    Electronic Resource
    Electronic Resource
    Freezing tolerance and avoidance in high-elevation Hawaiian plants (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 17 (1994), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Freezing resistance mechanisms were studied in five endemic Hawaiian species growing at high elevations on Haleakala volcano, Hawaii, where nocturnal subzero (°C) air temperatures frequently occur. Extracellular freezing occurred at around -5°C in leaves of Argyroxiphium sandwicense and Sophora chrysophylla, but these leaves can tolerate extracellular ice accumulation to -15°C and -12°C, respectively. Mucilage, which apparently acted as an ice nucleator, comprised 9 to 11% of the dry weight of leaf tissue in these two species. Leaves of Vaccinium reticulatum and Styphelia tameiameiae were also found to tolerate substantial extracellular freezing. Dubautia menziesii, on the other hand, exhibited the characteristics of permanent supercooling; a very rapid decline in liquid water content associated with simultaneous intracellular and extracellular freezing. However, in those species that tolerate extracellular freezing, the decline in liquid water content during freezing is relatively slow. Osmotic potential was lower at pre-dawn than at midday in four of the species studied. Nocturnal production of osmotically active solutes may have helped to prevent intracellular freeze dehydration as well as to provide non-colligative protection of cell membranes. Styphelia tameiameiae supercooled to -9·3°C and tolerated tissue freezing to below -15°C, a unique combination of physiological characteristics related to freezing. Tolerance of extracellular ice formation after considerable supercooling may have resulted from low tissue water content and a high degree of intracellular water binding in this species, as determined by nuclear magnetic resonance studies. The climate at high elevations in Hawaii is relatively unpredictable in terms of the duration of subzero temperatures and the lowest subzero temperature reached during the night. It appears that plants growing in this tropical alpine habitat have been under selective pressures for the evolution of freezing tolerance mechanisms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1994.tb02026.x
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  • 9
    Electronic Resource
    Electronic Resource
    Stomatal and environmental control of transpiration in a lowland tropical forest tree (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 16 (1993), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Stomatal control of crown transpiration was studied in Anacardium excelsum, a large-leaved, emergent canopy species common in the moist forests of Central and northern South America. A construction crane equipped with a gondola was used to gain access to the uppermost level in the crown of a 35-m-tall individual. Stomatal conductance at the single leaf scale, and transpiration and total vapour phase conductance (stomatal and boundary layer) at the branch scale were measured simultaneously using the independent techniques of porometry and stem heat balance, respectively. This permitted the sensitivity of transpiration to a marginal change in stomatal conductance to be evaluated using a dimensionless coupling coefficient (1-ω) ranging from zero to 1, with 1 representing maximal stomatal control of transpiration. Average stomatal conductance varied from 0.09 mol m−2 s−1 during the dry season to 0.3 mol m−2 s−1 during the wet season. Since boundary layer conductance was relatively low (0.4 mol m−2 s−1), 1-ω ranged from 0.46 during the dry season to only 0.25 during the wet season. A pronounced stomatal response to humidity was observed, which strongly limited transpiration as evaporative demand increased. The stomatal response to humidity was apparent only when the leaf surface was used as the reference point for measurement of external vapour pressure. Average transpiration was predicted to be nearly the same during the dry and wet seasons despite a 1 kPa difference in the prevailing leaf-to-air vapour pressure difference. The patterns of stomatal behaviour and transpiration observed were consistent with recent proposals that stomatal responses to humidity are based on sensing the transpiration rate itself.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1993.tb00889.x
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  • 10
    Electronic Resource
    Electronic Resource
    Apparent responses of stomata to transpiration and humidity in a hybrid poplar canopy (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 20 (1997), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: It has been proposed that the stomatal response to humidity relies on sensing of the transpiration rate itself rather than relative humidity or the saturation deficit per se. We used independent measurements of stomatal conductance (gs), transpiration (E), and leaf-to-air vapour pressure difference (V) in a hybrid poplar canopy to evaluate relationships between gs and E and between gs and V. Relationships between E, V and total vapour phase conductance or crown conductance (gc) were also assessed. Conductance measurements were made on exposed and partially shaded branches over a wide range of incident solar radiation. In exposed branches, gs appeared to decline linearly with increasing E and increasing V at both high and low irradiance. However, in a partially shaded branch, a bimodal relationship between gs and E was observed in which gs continued to decrease after E had reached a maximum value and begun to decrease. The relationship between gs and V for this branch was linear. Plots of gc against E always yielded bimodal or somewhat variable relationships, whereas plots of gc against V were invariably linear. It was not possible to derive a unique relationship between conductance and E or V because prevailing radiation partially determined the operating range for conductance. Normalization of data by radiation served to linearize responses observed within the same day or type of day, but even after normalization, data collected on partly cloudy days could not be used to predict stomatal behaviour on clear days and vice versa. An additional unidentified factor was thus also involved in determining operating ranges of conductance on days with different overall radiation regimes. We suggest that the simplest mechanism to account for the observed humidity responses is stomatal sensing of the epidermal or cuticular transpiration rate rather than the bulk leaf or stomatal transpiration rate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.1997.d01-18.x
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