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  • 1
    Digitale Medien
    Digitale Medien
    Relationship between plant hydraulic and biochemical properties derived from a steady-state coupled water and carbon transport model (2003)
    Oxford, UK : Blackwell Science, Ltd
    Plant, cell & environment 26 (2003), S. 0 
    Details
    ISSN: 1365-3040
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: There is growing evidence that plant stomata have evolved physiological controls to satisfy the demand for CO2 by photosynthesis while regulating water losses by leaves in a manner that does not cause cavitation in the soil–root–xylem hydraulic system. Whether the hydraulic and biochemical properties of plants evolve independently or whether they are linked at a time scale relevant to plant stand development remains uncertain. To address this question, a steady-state analytical model was developed in which supply of CO2 via the stomata and biochemical demand for CO2 are constrained by the balance between loss of water vapour from the leaf to the atmosphere and supply of water from the soil to the leaf. The model predicts the intercellular CO2 concentration (Ci) for which the maximum demand for CO2 is in equilibrium with the maximum hydraulically permissible supply of water through the soil–root–xylem system. The model was then tested at two forest stands in which simultaneous hydraulic, ecophysiological, and long-term carbon isotope discrimination measurements were available. The model formulation reproduces analytically recent findings on the sensitivity of bulk stomatal conductance (gs) to vapour pressure deficit (D); namely, gs = gref(1 − m × lnD), where m is a sensitivity parameter and gref is a reference conductance defined at D = 1 kPa. An immediate outcome of the model is an explicit relationship between maximum carboxylation capacity (Vcmax) and soil–plant hydraulic properties. It is shown that this relationship is consistent with measurements reported for conifer and rain forest angiosperm species. The analytical model predicts a decline in Vcmax as the hydraulic capacity of the soil–root–xylem decreases with stand development or age.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1365-3040.2003.00965.x
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    The effect of tree height on crown level stomatal conductance (2000)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 23 (2000), S. 0 
    Details
    ISSN: 1365-3040
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: Variation in stomatal conductance is typically explained in relation to environmental conditions. However, tree height may also contribute to the variability in mean stomatal conductance. Mean canopy stomatal conductance of individual tree crowns (GSi) was estimated using sap flux measurements in Fagus sylvatica L., and the hypothesis that GSi decreases with tree height was tested. Over 13 d of the growing season during which soil moisture was not limiting, GSi decreased linearly with the natural logarithm of vapour pressure deficit (D), and increased exponentially to saturation with photosynthetic photon flux density (Qo). Under conditions of D= 1 kPa and saturating Qo, GSi decreased by approximately 60% with 30 m increase in tree height. Over the same range in height, sapwood-to-leaf area ratio (AS:AL) doubled. A simple hydraulic model explained the variation in GSi based on an inverse relationship with height, and a linear relationship with AS:AL. Thus, in F. sylvatica, adjustments in AS:AL partially compensate for the negative effect of increased flow-path length on leaf conductance. Furthermore, because stomata with low conductance are less sensitive to D, gas exchange of tall trees is reduced less by high D. Despite these compensations, decreasing hydraulic conductance with tree height in F. sylvatica reduces carbon uptake through a corresponding decrease in stomatal conductance.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1365-3040.2000.00553.x
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Modelling the limits on the response of net carbon exchange to fertilization in a south-eastern pine forest (2002)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 25 (2002), S. 0 
    Details
    ISSN: 1365-3040
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: Using a combination of model simulations and detailed measurements at a hierarchy of scales conducted at a sandhills forest site, the effect of fertilization on net ecosystem exchange (NEE) and its components in 6-year-old Pinus taeda stands was quantified. The detailed measurements, collected over a 20-d period in September and October, included gas exchange and eddy covariance fluxes, sampled for a 10-d period each at the fertilized stand and at the control stand. Respiration from the forest floor and above-ground biomass was measured using chambers during the experiment. Fertilization doubled leaf area index (LAI) and increased leaf carboxylation capacity by 20%. However, this increase in total LAI translated into an increase of only 25% in modelled sunlit LAI and in canopy photosynthesis. It is shown that the same climatic and environmental conditions that enhance photosynthesis in the September and October periods also cause an increase in respiration The increases in respiration counterbalanced photosynthesis and resulted in negligible NEE differences between fertilized and control stands. The fact that total biomass of the fertilized stand exceeded 2·5 times that of the control, suggests that the counteracting effects cannot persist throughout the year. In fact, modelled annual carbon balance showed that gross primary productivity (GPP) increased by about 50% and that the largest enhancement in NEE occurred in the spring and autumn, during which cooler temperatures reduced respiration more than photosynthesis. The modelled difference in annual NEE between fertilized  and  control  stands  (approximately  200 1;g 2;C 3;m−2 y−1)  suggest that the effect of fertilization was sufficiently large to transform the stand from a net terrestrial carbon source to a net sink.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1365-3040.2002.00896.x
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    Water deficits and hydraulic limits to leaf water supply (2002)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 25 (2002), S. 0 
    Details
    ISSN: 1365-3040
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: Many aspects of plant water use – particularly in response to soil drought – may have as their basis the alteration of hydraulic conductance from soil to canopy. The regulation of plant water potential (Ψ) by stomatal control and leaf area adjustment may be necessary to maximize water uptake on the one hand, while avoiding loss of hydraulic contact with the soil water on the other. Modelling the changes in hydraulic conductance with pressure gradients in the continuum allows the prediction of water use as a function of soil environment and plant architectural and xylem traits. Large differences in water use between species can be attributed in part to differences in their ‘hydraulic equipment’ that is presumably optimized for drawing water from a particular temporal and spatial niche in the soil environment. A number of studies have identified hydraulic limits as the cause of partial or complete foliar dieback in response to drought. The interactions between root:shoot ratio, rooting depth, xylem properties, and soil properties in influencing the limits to canopy water supply can be used to predict which combinations should optimize water use in a given circumstance. The hydraulic approach can improve our understanding of the coupling of canopy processes to soil environment, and the adaptive significance of stomatal behaviour.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.0016-8025.2001.00799.x
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  • 5
    Digitale Medien
    Digitale Medien
    Influence of nutrient versus water supply on hydraulic architecture and water balance in Pinus taeda (2000)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 23 (2000), S. 0 
    Details
    ISSN: 1365-3040
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: We investigated the hydraulic consequences of a major decrease in root-to-leaf area ratio (AR:AL) caused by nutrient amendments to 15-year-old Pinus taeda L. stands on sandy soil. In theory, such a reduction in AR:AL should compromise the trees’ ability to extract water from drying sand. Under equally high soil moisture, canopy stomatal conductance (GS) of fertilized trees (F) was 50% that of irrigated/fertilized trees (IF), irrigated trees (I), and untreated control trees (C). As predicted from theory, F trees also decreased their stomatal sensitivity to vapour pressure deficit by 50%. The lower GS in F was associated with 50% reduction in leaf-specific hydraulic conductance (KL) compared with other treatments. The lower KL in F was in turn a result of a higher leaf area per sapwood area and a lower specific conductivity (conducting efficiency) of the plant and its root xylem. The root xylem of F trees was also 50% more resistant to cavitation than the other treatments. A transport model predicted that the lower AR:AL in IF trees resulted in a considerably restricted ability to extract water during drought. However, this deficiency was not exposed because irrigation minimized drought. In contrast, the lower AR:AL in F trees caused only a limited restriction in water extraction during drought owing to the more cavitation resistant root xylem in this treatment. In both fertilized treatments, approximate safety margins from predicted hydraulic failure were minimal suggesting increased vulnerability to drought-induced dieback compared with non-fertilized trees. However, IF trees are likely to be so affected even under a mild drought if irrigation is withheld.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1365-3040.2000.00625.x
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    Relationships between foliage and conducting xylem in Picea abies (L.) Karst. (1986)
    Springer
    Trees 1 (1986), S. 61-69 
    Details
    ISSN: 1432-2285
    Schlagwort(e): Branch cross-sectional area ; Leaf area ; Leaf biomass ; Picea abies ; Sapwood area
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Summary The relationship of leaf biomass and leaf area to the conductive area of stems and branches was investigated in Picea abies. A total of 30 trees were harvested to determine if these relationships were different in different crown zones and in trees growing with and without competition for light. Two methods were compared. In the first, data were accumulated from crown zones situated at the top of trees to the bottom; in the second, data were used from individual crown zones. The results indicated that the latter method is much more sensitive in detecting differences in the relationship of leaf biomass or leaf area to conductive area. The analysis also indicated that ratios such as leaf area/sapwood area are frequently size-dependent. This size-dependency can in some cases result in the differences being abscured, but more often leads to the false impression that the relationship between the variables changes. The relationship between leaf biomass and leaf area and conductive area of stems or branches was different in different crown zones and under different growth conditions. The slopes of these regressions appear to increase with decreasing transpirational demand and decrease with increasing hydraulic conductivity. The intercepts are probably related to the amount of identified sapwood actually involved in water conductance.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00197026
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    Uptake of water and solutes through twigs of Picea abies (L.) Karst (1989)
    Springer
    Trees 3 (1989), S. 33-37 
    Details
    ISSN: 1432-2285
    Schlagwort(e): P/V curve ; Picea abies ; Aerial uptake ; Bark permeability ; Mass flow
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Summary Uptake of water and magnesium chloride solution was investigated through the outer surface of twigs of Picea abies (L.) Karst. Water uptake was determined by using pressure/volume (P/V) curves of the twigs as a basis for calculation to avoid problems of superficial extraneous water. When water was sprayed on bark and needles of 3- to 7-year-old twigs at a xylem water potential of -1.00 MPa, they absorbed as much as 80 mm3 water in 200 min/g twig dry weight as the twig water potential recovered to -0.15 MPa. With fluorescent dyes, pathways for absorption of water and solutes through the twig bark were found, particularly through the radially orientated ray tissue. In addition to uptake by mass flow, magnesium could also diffuse along a concentration gradient from the twig surface into the xylem. In the field, the magnitude of these uptake processes would depend on the concentration of elements deposited by atmospheric precipitation, the concentration gradient between the plant surface and the xylem sap, the xylem water potential and the intensity and duration of each precipitation event.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00202398
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  • 8
    Digitale Medien
    Digitale Medien
    Influence of soil porosity on water use in Pinus taeda (2000)
    Springer
    Oecologia 124 (2000), S. 495-505 
    Details
    ISSN: 1432-1939
    Schlagwort(e): Key words  Pinus taeda ; Xylem cavitation ; Soil water transport ; Root-shoot relations ; Stomatal regulation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract  We analyzed the hydraulic constraints imposed on water uptake from soils of different porosities in loblolly pine (Pinus taeda L.) by comparing genetically related and even-aged plantations growing in loam versus sand soil. Water use was evaluated relative to the maximum transpiration rate (E crit) allowed by the soil-leaf continuum. We expected that trees on both soils would approach E crit during drought. Trees in sand, however, should face greater drought limitation because of steeply declining hydraulic conductivity in sand at high soil water potential (Ψ S). Transport considerations suggest that trees in sand should have higher root to leaf area ratios (A R:A L), less negative leaf xylem pressure (Ψ L), and be more vulnerable to xylem cavitation than trees in loam. The A R:A L was greater in sand versus loam (9.8 vs 1.7, respectively). This adjustment maintained about 86% of the water extraction potential for both soils. Trees in sand were more deeply rooted (〉1.9 m) than in loam (95% of roots 〈0.2 m), allowing them to shift water uptake to deeper layers during drought and avoid hydraulic failure. Midday Ψ L was constant for days of high evaporative demand, but was less negative in sand (–1.6 MPa) versus loam (–2.1 MPa). Xylem was more vulnerable to cavitation in sand versus loam trees. Roots in both soils were more vulnerable than stems, and experienced the greatest predicted loss of conductivity during drought. Trees on both soils approached E crit during drought, but at much higher Ψ S in sand (〈–0.4 MPa) than in loam (〈–1.0 MPa). Results suggest considerable phenotypic plasticity in water use traits for P. taeda which are adaptive to differences in soil porosity.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/PL00008875
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  • 9
    Digitale Medien
    Digitale Medien
    Performance of two Picea abies (L.) Karst. stands at different stages of decline (1988)
    Springer
    Oecologia 76 (1988), S. 513-518 
    Details
    ISSN: 1432-1939
    Schlagwort(e): Picea abies ; Forest decline ; Stomatal response ; Photosynthesis ; Mg-deficiency
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary CO2 assimilation rate (A) and leaf conductance (g) were measured in the field on intact branches of 35-year-old Picea abies (L.) Karst. trees, in five plots each in a healthy and a declining stand. The declining site included trees with yellow needles. In order to separate atmospheric effects on gas exchange from effects of nutrient deficiency, direct effects of atmospheric pollutants were studied on green needles of different age classes in plots of trees at different stages of visible decline. The effects of nutrient deficiency on gas exchange were studied on a different group of trees showing needles of various degrees of yellowing. CO2 assimilation of green needles at the same leaf conductance fell somewhat only when needles had reached 5 years of age, the oldest age examined in this study. Leaf conductance decreased with increasing needle age, but green needles in the declining stand had leaf conductances similar to those of needles in the healthy stand. Stomata of needles with different magnesium concentrations responded to light and air humidity in all age classes. Thus, as long as needles were green, no dese effect was detectable up to 5 years of exposure to atmospheric emissions. Since all needles, green and yellow, were exposed to the same pollution levels, differences in gas exchange between green and yellow needles could not be explained simply in terms of long-term direct effects of air pollution. Needle magnesium contents were correlated with needle yellowing. Neither needle color change nor the magnesium concentration were related to g, but CO2 uptake at ambient CO2 levels declined with lower magnesium concentration and greater degrees of needle yellowing.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00397862
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
    Digitale Medien
    Digitale Medien
    Performance of two Picea abies (L.) Karst. stands at different stages of decline (1988)
    Springer
    Oecologia 75 (1988), S. 25-37 
    Details
    ISSN: 1432-1939
    Schlagwort(e): Forest decline ; Carbohydrates ; Picea abies ; Growth ; Leaf area index
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary This is the first in a series of papers on the growth, photosynthetic rate, water and nutrient relations, root distribution and mycorrhizal frequency of two Norway spruce forests at different stages of decline. One of the stands was composed of green trees only while the other included trees ranging in appearance from full green crowns to thin crowns with yellow needles. In this paper we compare the growth and carbohydrate relations of the two stands and examine relationships among growth variables in ten plots. The declining stand produced 65 percent of the wood per ground area compared with the stand in which all trees were green because its foliage produced less wood at any level of leaf area index. The difference in foliage efficiency between the sites could not be explained by differeneces in climate, competition or stand structure. The declining stand appeared to have lower carbon gain as indicated by a smaller increase in reserve carbohydrates before bud break, and weaker sinks for carbohydrates as indicated by less use of the stored carbohydrates than the healthy stand. Thus, growth reduction was probably related to factors which affect both photosynthesis and, even more, the sinks for carbohydrate.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00378810
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