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Leaf Water Potential (leaf + water_potential)

Distribution by Scientific Domains

Life Sciences	91%
2 Other Domains	9%

Distribution within Life Sciences

Plant Science	57%
Ecology & Organismal Biology	27%
Plant Pathology	12%

Selected Abstracts

Foliar dehydration tolerance of mycorrhizal cowpea, soybean and bush bean

NEW PHYTOLOGIST, Issue 2 2001
Robert M. Augé
Summary ,,Foliar dehydration tolerance of three mycorrhizal and nonmycorrhizal legumes is presented here. ,,Leaf water potential, osmotic adjustment and soil matric potential at the end of a lethal drying episode were compared in soybean, cowpea and bush bean colonized or uncolonized by Glomus intraradices. ,,Lethal leaf water potential were similar among treatments except in soybean, for which nonmycorrhizal plants given low phosphorus fertilization had values 0.3,0.4 MPa lower than mycorrhizal plants or nonmycorrhizal plants given higher phosphorus fertilization. Mycorrhizal symbiosis did not affect osmotic adjustment or lethal soil matric potential. Nonmycorrhizal cowpeas given low phosphorus showed more osmotic adjustment than nonmycorrhizal cowpeas given higher phosphorus. Foliage of host species typically classified as drought avoiders, cowpea and bush bean, survived to lower soil matric potentials than soybean, although soybean foliage was more tolerant of dehydration. ,,Our findings support the idea that when arbuscular mycorrhizal plants fare better than nonmycorrhizal plants during drought, it is probably due to enhanced drought avoidance capabilities conferred by the symbiosis rather than to changes in ability of foliage to withstand dehydration. [source]

Ecophysiology of Eucalyptus marginata and Corymbia calophylla in decline in an urban parkland

AUSTRAL ECOLOGY, Issue 5 2009
ALASDAIR GRIGG
Abstract Eucalypt trees are in decline throughout urban landscapes of south western Australia. This study investigated the cause of decline in Eucalyptus marginata and Corymbia calophylla trees in parkland and compared water and nutrient relations with healthy trees in adjacent bushland in Perth, Western Australia. It was hypothesized that: (i) trees were drought stressed through competition for soil water by the vigorous turf; (ii) excessive uptake of nitrogen, because of fertilizer application to turf, caused toxicity; and/or (iii) micronutrient (Cu, Fe, Mn and/or Zn) deficit was induced by high-pH irrigation water applied to turf around parkland trees. Leaf water potential showed aseasonal variation in the irrigated parkland trees and foliar ,13C indicated that parkland trees generally had low water-use efficiency and were not drought stressed relative to bushland trees. Foliar N levels were not significantly different between parkland and bushland trees indicating that excess N uptake was not a factor in the decline. Foliar total Fe, ,metabolically active' Fe, Cu and Zn concentrations were not significantly different between parkland and bushland trees. Foliar manganese concentrations were indicative of deficiency and significantly lower in parkland trees (5,14 µg g,1) relative to bushland trees (22,35 µg g,1). It is concluded that application of alkaline irrigation water to the parkland site reduced the plant-availability of Mn; however, our study of only one parkland site does not allow us to generalize the results across other parklands. [source]

Suppression of ectomycorrhizal development in young Pinus thunbergii trees inoculated with Bursaphelenchus xylophilus

FOREST PATHOLOGY, Issue 3 2001
Ichihara
In order to study the changes in ectomycorrhizal development during symptom expression of pine wilt disease, root window observations were conducted concurrent with measurements of leaf water potential as well as photosynthetic and transpiration rates of 5-year-old Pinus thunbergii trees that were inoculated with the pinewood nematode (PWN) Bursaphelenchus xylophilus. Infected trees were compared with girdled and uninfected control trees. Ectomycorrhizas developed constantly during the experimental period in control trees but did not develop in the girdled trees. Ectomycorrhizal development ceased within 2 weeks in those trees that finally died after PWN infection. In the trees that survived PWN infection, ectomycorrhizal development ceased within 1,4 weeks of inoculation but was resumed thereafter within 3,6 weeks. Ectomycorrhizal development ceased prior to a decrease in both photosynthetic rate and leaf water potential in the inoculated trees. Restriction du développement ectomycorhizien chez de jeunes Pinus thunbergii inoculés par Bursaphelenchus xylophilus Pour étudier les modifications du développement ectomycorhizien durant l'évolution des symptômes de flétrissement des pins, un suivi des racines a été réalisé en parallèle avec des mesures du potentiel hydrique foliaire, de la photosynthèse et de la transpiration chez des Pinus thunbergiiâgés de 5 ans inoculés avec le nématode des pins (PWN), Bursaphelenchus xylophilus. Des arbres infectés ont été comparés à des arbres cernés et des témoins non infectés. Les ectomycorhizes se sont développées de façon constante durant la période d'observation chez les arbres témoins mais non pas chez les arbres cernés. Le développement ectomycorhizien s'était arrêté en 2 semaines chez les arbres qui sont morts de l'infection du PWN. Chez les arbres qui ont survécu à l'infection du PWN, le développement ectomycorhizien avait cessé 1 à 4 semaines après l'inoculation mais avait repris ensuite entre la 3ème et la 6ème semaine. Le développement ectomycorhizien cessait avant la diminution de la photosynthèse et du potentiel hydrique foliaire chez les arbres inoculés. Unterdrückung der Ektomykorrhizabildung in jungen Pinus thunbergii nach Inokulation mit Bursaphelenchus xylophilus Um Veränderungen der Ektomykorrhizabildung während der Symptomausprägung der Kiefernwelke zu untersuchen, wurde diese mit Hilfe von ,Wurzelfenstern' beobachtet. Gleichzeitig wurde das Wasserpotential der Blätter sowie die Photosynthese- und Transpirationsraten fünfjähriger Pinus thunbergii gemessen, die mit dem Erreger der Kiefernwelke (PWN) Bursaphelenchus xylophilus inokuliert worden waren. Die infizierten Bäume wurden mit geringelten Bäumen und mit nicht infizierten Kontrollen verglichen. In den Kontrollbäumen entwickelten sich während des gesamten Beobachtungszeitraumes kontinuierlich Ektomykorrhizen, es bildeten sich jedoch keine bei den geringelten Bäumen. Die Ektomykorrhizabildung hörte bei den Bäumen, die nach der PWN-Infektion schliesslich abstarben, innerhalb von zwei Wochen auf. Bei Bäumen, welche die PWN-Infektion überlebten, war die Ektomykorrhizabildung ein bis vier Wochen nach der Inokulation unterbrochen, sie wurde aber nach drei bis sechs Wochen wieder fortgesetzt. Die Bildung der Ektomykorrhiza hörte in den inokulierten Bäumen auf, bevor die Photosyntheserate und das Wasserpotential in den Blättern abnahmen. [source]

Stem hydraulics mediates leaf water status, carbon gain, nutrient use efficiencies and plant growth rates across dipterocarp species

FUNCTIONAL ECOLOGY, Issue 4 2009
Jiao-Lin Zhang
Summary 1Stem vascular system strongly influences structure and functioning of leaves, life-history, and distribution of plants. Xylem structure and hydraulic conductivity of branches, leaf functional traits, and growth rates in 17 dipterocarp species in a mature plantation stand were examined to explore the functional relationships between these traits. 2Maximum hydraulic conductivity on the bases of both sapwood and leaf area (kL) were positively correlated with midday leaf water potential in the rainy season, stomatal conductance, area-based maximum photosynthetic rate, photosynthetic N (PNUE) and P use efficiencies (PPUE), and mean height and diameter growth rates. Moreover, kL was positively correlated with mesophyll thickness and mass-based maximum photosynthetic rate. These results revealed the mechanistic linkage between stem hydraulics and leaf photosynthesis through nutrient use efficiency and mesophyll development of leaves. 3A detrended correspondence analysis (DCA) using 37 traits showed that the traits related to stem hydraulics and leaf carbon gain were loaded on the first axis whereas traits related to light harvesting were loaded on the second axis, indicating that light harvesting is a distinct ecological axis for tropical canopy plants. The DCA also revealed a trade-off between photosynthetic water use efficiency and hydraulic conductivity along with PNUE and PPUE. 4The congeneric species were scattered fairly close together on the DCA diagram, indicating that the linkages between stem hydraulics, leaf functional traits, and plant growth rates are phylogenetically conserved. 5These results suggest that stem hydraulics mediates leaf water status, carbon gain, nutrient use efficiencies, and growth rates across the dipterocarp species. The wide variation in functional traits and growth rates among these dipterocarp species along with the trade-offs mentioned above provide a possible explanation for their co-existence in tropical forest communities. [source]

Below-ground hydraulic conductance is a function of environmental conditions and tree size in Scots pine

FUNCTIONAL ECOLOGY, Issue 6 2007
J. MARTÍNEZ-VILALTA
Summary 1Variations in water tension in a transpiring tree cause elastic changes in stem diameter. To better understand the dynamics of these variations, stem diameter changes and sap flow rates were monitored simultaneously in trees from two Scots pine chronosequences in Scotland. 2Tree below-ground hydraulic conductance (kbg) was estimated from the relationship between leaf-specific sap flow rates and the difference between stem and soil water potentials estimated from diameter variations in the stem. 3In a given tree, kbg varied both within and among days, with conductance increasing as a function of sap flow and evaporative demand. These patterns could be explained in terms of a composite model of root water transport and possible changes in the gating of aquaporins. 4We interpreted these trends of increasing kbg with evaporative demand as a mechanism to enhance the ability of trees to control leaf water potential and keep it within physiologically acceptable limits, with potential implications for our general understanding of plant water relations, and for the estimation and modelling of ecosystem water fluxes. 5Across trees, kbg declined with increasing tree age/size, but the proportional contribution of below-ground to whole-tree hydraulic resistance also declined. This is consistent with an increase in below-ground carbon allocation in old/tall trees and a partial acclimation of tall trees to hydraulic limitations. It is argued that these trends have to be considered when discussing the importance of tree height for water transport and growth. [source]

Forced depression of leaf hydraulic conductance in situ: effects on the leaf gas exchange of forest trees

FUNCTIONAL ECOLOGY, Issue 4 2007
T. J. BRODRIBB
Summary 1Recent work on the hydraulic conductance of leaves suggests that maximum photosynthetic performance of a leaf is defined largely by its plumbing. Pursuing this idea, we tested how the diurnal course of gas exchange of trees in a dry tropical forest was affected by artificially depressing the hydraulic conductance of leaves (Kleaf). 2Individual leaves from four tropical tree species were exposed to a brief episode of forced evaporation by blowing warm air over leaves in situ. Despite humid soil and atmospheric conditions, this caused leaf water potential (,leaf) to fall sufficiently to induce a 50,74% drop in Kleaf. 3Two of the species sampled proved highly sensitive to artificially depressed Kleaf, leading to a marked and sustained decline in the instantaneous rate of CO2 uptake, stomatal conductance and transpiration. Leaves of these species showed a depression of hydraulic and photosynthetic capacity in response to the ,blow-dry' treatment similar to that observed when major veins in the leaf were severed. 4By contrast, the other two species sampled were relatively insensitive to Kleaf manipulation; photosynthetic rates were indistinguishable from control (untreated) leaves 4 h after treatment. These insensitive species demonstrate a linear decline of Kleaf with ,leaf, while Kleaf in the two sensitive species falls precipitously at a critical water deficit. 5We propose that a sigmoidal Kleaf vulnerability enables a high diurnal yield of CO2 at the cost of exposing leaves to the possibility of xylem cavitation. Linear Kleaf vulnerability leads to a relatively lower CO2 yield, while providing better protection against cavitation. [source]

Effect Of Height On Tree Hydraulic Conductance Incompletely Compensated By Xylem Tapering

FUNCTIONAL ECOLOGY, Issue 2 2005
S. ZAEHLE
Summary 1The hydraulic limitation theory proposes that the decline of forest productivity with age is a consequence of the loss of whole-plant and leaf-specific hydraulic conductance with tree height caused by increased friction. Recent theoretical analyses have suggested that tapering (the broadening of xylem vessel diameter from terminal branches to the base of the stem) could compensate completely for the effect of tree height on hydraulic conductance, and thus on tree growth. 2The data available for testing this hypothesis are limited, but they do not support the implication that whole-tree and leaf-specific hydraulic conductance are generally independent of tree height. Tapering cannot exclude hydraulic limitation as the principle mechanism for the observed decline in growth. 3Reduction of the leaf-to-sapwood area ratio, decreased leaf water potential, loss of leaf-cell turgor, or osmotic adjustments in taller trees could reduce the effect of increased plant hydraulic resistance on stomatal conductance with height. However, these mechanisms operate with diminishing returns, as they infer increased costs to the tree that will ultimately limit tree growth. To understand the decline in forest growth, the effects of these acclimation mechanisms on carbon uptake and allocation should be considered. [source]

Hydraulic differentiation of Ponderosa pine populations along a climate gradient is not associated with ecotypic divergence

FUNCTIONAL ECOLOGY, Issue 4 2002
H. Maherali
Summary 1.,Pinus ponderosa occurs in a range of contrasting environments in the western USA. Xeric populations typically have lower leaf : sapwood area ratio (AL/AS) and higher whole-tree leaf specific hydraulic conductance (KL) than mesic populations. These climate-driven shifts in hydraulic architecture are considered adaptive because they maintain minimum leaf water potential above levels that cause xylem cavitation. 2.,Using a common garden study, we examined whether differences in biomass allocation and hydraulic architecture between P. ponderosa populations originating from isolated outcrops in the Great Basin desert and Sierran montane environments were caused by ecotypic differentiation or phenotypic plasticity. To determine if populations were genetically differentiated and if phenotypic and genetic differentiation coincided, we also characterized the genetic structure of these populations using DNA microsatellites. 3.,Phenotypic differentiation in growth, biomass allocation and hydraulic architecture was variable among populations in the common garden. There were no systematic differences between desert and montane climate groups that were consistent with adaptive expectations. Drought had no effect on the root : shoot and needle : stem ratio, but reduced seedling biomass accumulation, leaf area ratio, AL/AS and KL. Stem hydraulic conductance (KH) was strongly size-dependent, and was lower in droughted plants, primarily because of lower growth. 4.,Although microsatellites were able to detect significant non-zero (P < 0·001) levels of differentiation between populations, these differences were small and were not correlated with geographic separation or climate group. Estimates of genetic differentiation among populations were low (<5%), and almost all the genetic variation (>95%) resided within populations, suggesting that gene flow was the dominant factor shaping genetic structure. 5.,These results indicate that biomass allocation and hydraulic differences between desert and montane populations are not the result of ecotypic differentiation. Significant drought effects on leaf : sapwood allocation and KL suggest that phenotypic differentiation between desert and montane climates could be the result of phenotypic plasticity. [source]

Increased leaf area dominates carbon flux response to elevated CO2 in stands of Populus deltoides (Bartr.)

GLOBAL CHANGE BIOLOGY, Issue 5 2005
Ramesh Murthy
Abstract We examined the effects of atmospheric vapor pressure deficit (VPD) and soil moisture stress (SMS) on leaf- and stand-level CO2 exchange in model 3-year-old coppiced cottonwood (Populus deltoides Bartr.) plantations using the large-scale, controlled environments of the Biosphere 2 Laboratory. A short-term experiment was imposed on top of continuing, long-term CO2 treatments (43 and 120 Pa), at the end of the growing season. For the experiment, the plantations were exposed for 6,14 days to low and high VPD (0.6 and 2.5 kPa) at low and high volumetric soil moisture contents (25,39%). When system gross CO2 assimilation was corrected for leaf area, system net CO2 exchange (SNCE), integrated daily SNCE, and system respiration increased in response to elevated CO2. The increases were mainly as a result of the larger leaf area developed during growth at high CO2, before the short-term experiment; the observed decline in responses to SMS and high VPD treatments was partly because of leaf area reduction. Elevated CO2 ameliorated the gas exchange consequences of water stress at the stand level, in all treatments. The initial slope of light response curves of stand photosynthesis (efficiency of light use by the stand) increased in response to elevated CO2 under all treatments. Leaf-level net CO2 assimilation rate and apparent quantum efficiency were consistently higher, and stomatal conductance and transpiration were significantly lower, under high CO2 in all soil moisture and VPD combinations (except for conductance and transpiration in high soil moisture, low VPD). Comparisons of leaf- and stand-level gross CO2 exchange indicated that the limitation of assimilation because of canopy light environment (in well-irrigated stands; ratio of leaf : stand=3.2,3.5) switched to a predominantly individual leaf limitation (because of stomatal closure) in response to water stress (leaf : stand=0.8,1.3). These observations enabled a good prediction of whole stand assimilation from leaf-level data under water-stressed conditions; the predictive ability was less under well-watered conditions. The data also demonstrated the need for a better understanding of the relationship between leaf water potential, leaf abscission, and stand LAI. [source]

Water Deficit Reduced Fertility of Young Microspores Resulting in a Decline of Viable Mature Pollen and Grain Set in Rice

JOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 1 2009
G. N. Nguyen
Abstract Pollen formation in rice (Oryza sativa L.) is highly vulnerable to environmental stresses such as heat, chilling and drought. In rice plants exposed to drought during male reproductive development, the most obvious damage often observed is a decline in the number of engorged pollen and grain set. This has been well characterized in rice under chilling and to a lesser extent under drought stress. Moreover, detailed literature on the immediate effects of drought on developing young microspores in rice is still limited. Here, we report findings from experiments on rice plants exposed to water deficit for three consecutive days during early stages of anther development. When the osmotic potential of the growing medium was equal to or less than ,0.5 MPa, as induced by polyethylene glycol, the leaf water potential was significantly lowered and grain set was reduced. A strong correlation between grain set and viable young microspores (P < 0.001, r2 = 0.8223) indicates that water deficit immediately reduced fertility of rice plants at the time of exposure. This result suggests a new underlying mechanism of water deficit-induced pollen abortion in rice. [source]

Physiological and biochemical traits involved in the genotypic variability to salt tolerance of Tunisian Cakile maritima

AFRICAN JOURNAL OF ECOLOGY, Issue 4 2009
Megdiche Wided
Abstract Cakile maritima (family: Brassicaceae) was collected from three provenances belonging to different bioclimatic stages (humid, semi arid and arid) in Tunisia to study their eco-physiological and biochemical responses to salinity. Seedlings were cultivated on inert sand for 20 days under NaCl treatments (0, 100, 200, 400 mm NaCl). Plant response to salinity was provenance- and salt-dependent. At 100 mm NaCl, growth parameters (leaf biomass, area, number per plant and relative growth rate) were improved in plants from Jerba (originating from arid bioclimatic stage) compared with the control, while growth was reduced in those from Tabarka (from humid area). High salt levels (400 mm NaCl) decreased the plant growth in the three provenances, but plants in Tabarka were the most salt sensitive. The relative salt tolerance of plants from Jerba and Bekalta provenances was associated with low levels of malondialdehyde as well as of electrolyte leakage and endoproteolytic activity. Salt reduced leaf hydration, the decrease in water content being dose-dependent and more pronounced in Tabarka. Increase in salinity led to significant increase in leaf succulence and decrease in leaf water potential, especially in Jerba plants. The plants from the latter displayed the highest leaf levels of Na+ and Cl,, proline, soluble carbohydrates, soluble proteins, and polyphenols. Overall, the higher salt tolerance of plants from Jerba provenance, and to a lower extent of those from Bekalta, may be partly related to their better capacity for osmotic adjustment and to limit oxidative damage when salt-challenged. Résumé Cakile maritima a été collecté (famille des Brassicaceae) dans trois provenances appartenant à des étages bioclimatiques différentes (humide, semi-aride et aride) de la Tunisie, dans le but d'étudier leurs réponses éco-physiologique et biochimique à la salinité. Des plantules ont été cultivées dans du sable inerte pendant vingt jours avec des doses croissantes de NaCl (0, 100, 200 et 400 mm NaCl). La réponse de Cakile maritima dépend de la provenance et de la salinité du milieu. A 100 mm de NaCl, les paramètres de croissance (biomasse, surface et nombre des feuilles par plante ainsi que le taux de la croissance relative) ont été améliorés chez Djerba (zone bioclimatique aride) par comparaison aux plantes témoins, tandis que la croissance a été réduite chez Tabarka (zone humide). A la plus forte dose de sel (400 mm), une réduction de la croissance des trois provenances a été enregistrée avec une nette sensibilité chez les plantes de la provenance Tabarka. La tolérance relative des deux provenances Djerba et Bekalta est associée à une faible teneur en malondialdéhyde ainsi qu'une fuite d'électrolyte et activité endo-protéolytique modérées. Le traitement salin a réduit l'hydratation des feuilles et cette diminution du contenu en eau est dose-dépendante et elle est plus prononcée chez Tabarka. En outre, l'augmentation de la salinité du milieu a entrainé une élévation de la succulence des feuilles concomitante à une diminution du potentiel hydrique notamment chez Djerba. Les plantes de cette dernière ont été les plus riches en Na+ et Cl - , en proline, carbohydrates, en protéines solubles et en polyphénols. En général, la tolérance au sel de la provenance Djerba, et à moindre degré Bekalta, est en partie reliée à la meilleure capacité d'ajustement osmotique et la limitation des dommages oxydatifs sous stress salin. [source]

Effect of Chestnut Ink Disease on Photosynthetic Performance

JOURNAL OF PHYTOPATHOLOGY, Issue 3 2004
J. Gomes-Laranjo
Abstract In order to evaluate the evolutionary impact of chestnut ink disease, infected trees (cv. Judia), were compared with non-infected trees, in three separate months: July, September and October. The aim of this work is to analyse the effects of the infection using parameters related to plant water relations, gas exchange and biometric data of leaves and fruits. In this period, temperatures decreased from 31 to 16°C contrarily to precipitation, which increased from 18 to 178 mm, respectively. In consequence, leaf water potential changed between ,1.6 and ,1.0 MPa while in infected plants the values maintained around ,1.2 MPa over the referred period. Nevertheless, at the gas exchanges level, differences in stomatal conductance, transpiration and photosynthesis were only detected in October. Concerning photosynthesis rate, the infected plants showed, in relation to September, a reduction around 35% whereas in non-infected plants the decline was 25%. Alterations in the chlorophyll contents were also observed between September and October. In infected plants reduction on total amount of chlorophyll was from 18.6 to 13.4 mg/Wf, while in non-infected plants values were only decayed from 15.1 to 13.1 mg/Wf. In relation to chlorophyll a/chlorophyll b ratio, plants infected by the oomycete preserved values in the level of 2.6, whereas in healthy plants values changed from 2.5 to 2.3. Leaves and fruits from infected chestnut trees were 13 and 20% smaller, respectively than those from non-infected. Fruits from infected plants also had less starch but more crude protein. [source]

Foliar dehydration tolerance of mycorrhizal cowpea, soybean and bush bean

Rice leaf growth and water potential are resilient to evaporative demand and soil water deficit once the effects of root system are neutralized

PLANT CELL & ENVIRONMENT, Issue 8 2010
BORIS PARENT
ABSTRACT Rice is known to be sensitive to soil water deficit and evaporative demand, with a greatest sensitivity of lowland-adapted genotypes. We have analysed the responses of plant water relations and of leaf elongation rate (LER) to soil water status and evaporative demand in seven rice genotypes belonging to different species, subspecies, either upland- or lowland-adapted. In the considered range of soil water potential (0 to ,0.6 MPa), stomatal conductance was controlled in such a way that the daytime leaf water potential was similar in well-watered, droughted or flooded conditions (isohydric behaviour). A low sensitivity of LER to evaporative demand was observed in the same three conditions, with small differences between genotypes and lower sensitivity than in maize. The sensitivity of LER to soil water deficit was similar to that of maize. A tendency towards lower sensitivities was observed in upland than lowland genotypes but with smaller differences than expected. We conclude that leaf water status and leaf elongation of rice are not particularly sensitive to water deficit. The main origin of drought sensitivity in rice may be its poor root system, whose effect was alleviated in the study presented here by growing plants in pots whose soil was entirely colonized by roots of all genotypes. [source]

Effects of hydraulic architecture and spatial variation in light on mean stomatal conductance of tree branches and crowns

PLANT CELL & ENVIRONMENT, Issue 4 2007
B. E. EWERS
ABSTRACT In a Pinus taeda L. (loblolly pine) plantation, we investigated whether the response to vapour pressure deficit (D) of canopy average stomatal conductance (GS) calculated from sap flux measured in upper and lower branches and main stems follows a hydraulically modelled response based on homeostasis of minimum leaf water potential (,L). We tested our approach over a twofold range of leaf area index (L; 2,4 m2 m,2) created by irrigation, fertilization, and a combination of irrigation and fertilization relative to untreated control. We found that GS scaled well from leaf-level porometery [porometry-based stomatal conductance (gs)] to branch-estimated and main stem-estimated GS. The scaling from branch- to main stem-estimated GS required using a 45 min moving average window to extract the diurnal signal from the large high-frequency variation, and utilized a light attenuation model to weigh the contribution of upper and lower branch-estimated GS. Our analysis further indicated that, regardless of L, lower branch-estimated GS represented most of the main stem-estimated GS in this stand. We quantified the variability in both upper and lower branch-estimated GS by calculating the SD of the residuals from a moving average smoothed diurnal. A light model, which incorporated penumbral effects on vertical distribution of direct light, was employed to estimate the variability in light intensity at each canopy level in order to explain the increasing SD of both upper and lower branch-estimated GS with light. The results from the light model showed that the upper limit of the variability in individual branch-estimated GS could be attributed to incoming light, but not the variation below that upper limit. A porous medium model of water flow in trees produced a pattern of variation below the upper limit that was consistent with the observed variability in branch-estimated GS. Our results indicated that stems acted to buffer leaf- and branch-level variation and might transmit a less-variable water potential signal to the roots. [source]

Biophysical properties and functional significance of stem water storage tissues in Neotropical savanna trees

PLANT CELL & ENVIRONMENT, Issue 2 2007
FABIAN G. SCHOLZ
ABSTRACT Biophysical characteristics of sapwood and outer parenchyma water storage compartments were studied in stems of eight dominant Brazilian Cerrado tree species to assess the impact of differences in tissue capacitance on whole-plant water relations. The rate of decline in tissue water potential with relative water content (RWC) was greater in the outer parenchyma than in the sapwood for most of the species, resulting in tissue-and species-specific differences in capacitance. Sapwood capacitance on a tissue volume basis ranged from 40 to 160 kg m,3 MPa,1, whereas outer parenchyma capacitance ranged from 25 to only 60 kg m,3 MPa,1. In addition, osmotic potentials at full turgor and at the turgor loss point were more negative for the outer parenchyma compared with the sapwood, and the maximum bulk elastic modulus was higher for the outer parenchyma than for the sapwood. Sapwood capacitance decreased linearly with increasing sapwood density across species, but there was no significant correlation between outer parenchyma capacitance and tissue density. Midday leaf water potential, the total hydraulic conductance of the soil/leaf pathway and stomatal conductance to water vapour (gs) all increased with stem volumetric capacitance, or with the relative contribution of stored water to total daily transpiration. However, the difference between the pre-dawn water potential of non-transpiring leaves and the weighted average soil water potential, a measure of the water potential disequilibrium between the plant and soil, increased asymptotically with total stem capacitance across species, implying that overnight recharge of water storage compartments was incomplete in species with greater capacitance. Overall, stem capacitance contributes to homeostasis in the diurnal and seasonal water balance of Cerrado trees. [source]

Evidence from Amazonian forests is consistent with isohydric control of leaf water potential

PLANT CELL & ENVIRONMENT, Issue 2 2006
ROSIE A. FISHER
ABSTRACT Climate modelling studies predict that the rain forests of the Eastern Amazon basin are likely to experience reductions in rainfall of up to 50% over the next 50,100 years. Efforts to predict the effects of changing climate, especially drought stress, on forest gas exchange are currently limited by uncertainty about the mechanism that controls stomatal closure in response to low soil moisture. At a through-fall exclusion experiment in Eastern Amazonia where water was experimentally excluded from the soil, we tested the hypothesis that plants are isohydric, that is, when water is scarce, the stomata act to prevent leaf water potential from dropping below a critical threshold level. We made diurnal measurements of leaf water potential (,l), stomatal conductance (gs), sap flow and stem water potential (,stem) in the wet and dry seasons. We compared the data with the predictions of the soil,plant,atmosphere (SPA) model, which embeds the isohydric hypothesis within its stomatal conductance algorithm. The model inputs for meteorology, leaf area index (LAI), soil water potential and soil-to-leaf hydraulic resistance (R) were altered between seasons in accordance with measured values. No optimization parameters were used to adjust the model. This ,mechanistic' model of stomatal function was able to explain the individual tree-level seasonal changes in water relations (r2 = 0.85, 0.90 and 0.58 for ,l, sap flow and gs, respectively). The model indicated that the measured increase in R was the dominant cause of restricted water use during the dry season, resulting in a modelled restriction of sap flow four times greater than that caused by reduced soil water potential. Higher resistance during the dry season resulted from an increase in below-ground resistance (including root and soil-to-root resistance) to water flow. [source]

Stomatal sensitivity to vapour pressure difference over a subambient to elevated CO2 gradient in a C3/C4 grassland

PLANT CELL & ENVIRONMENT, Issue 8 2003
H. MAHERALI
ABSTRACT In the present study the response of stomatal conductance (gs) to increasing leaf-to-air vapour pressure difference (D) in early season C3 (Bromus japonicus) and late season C4 (Bothriochloa ischaemum) grasses grown in the field across a range of CO2 (200,550 µmol mol,1) was examined. Stomatal sensitivity to D was calculated as the slope of the response of gs to the natural log of externally manipulated D (dgs/dlnD). Increasing D and CO2 significantly reduced gs in both species. Increasing CO2 caused a significant decrease in stomatal sensitivity to D in Br. japonicus, but not in Bo. ischaemum. The decrease in stomatal sensitivity to D at high CO2 for Br. japonicus fit theoretical expectations of a hydraulic model of stomatal regulation, in which gs varies to maintain constant transpiration and leaf water potential. The weaker stomatal sensitivity to D in Bo. ischaemum suggested that stomatal regulation of leaf water potential was poor in this species, or that non-hydraulic signals influenced guard cell behaviour. Photosynthesis (A) declined with increasing D in both species, but analyses of the ratio of intercellular to atmospheric CO2 (Ci/Ca) suggested that stomatal limitation of A occurred only in Br. japonicus. Rising CO2 had the greatest effect on gs and A in Br. japonicus at low D. In contrast, the strength of stomatal and photosynthetic responses to CO2 were not affected by D in Bo. ischaemum. Carbon and water dynamics in this grassland are dominated by a seasonal transition from C3 to C4 photosynthesis. Interspecific variation in the response of gs to D therefore has implications for predicting seasonal ecosystem responses to CO2. [source]

A coupled model of stomatal conductance, photosynthesis and transpiration

PLANT CELL & ENVIRONMENT, Issue 7 2003
A. TUZET
ABSTRACT A model that couples stomatal conductance, photosynthesis, leaf energy balance and transport of water through the soil,plant,atmosphere continuum is presented. Stomatal conductance in the model depends on light, temperature and intercellular CO2 concentration via photosynthesis and on leaf water potential, which in turn is a function of soil water potential, the rate of water flow through the soil and plant, and on xylem hydraulic resistance. Water transport from soil to roots is simulated through solution of Richards' equation. The model captures the observed hysteresis in diurnal variations in stomatal conductance, assimilation rate and transpiration for plant canopies. Hysteresis arises because atmospheric demand for water from the leaves typically peaks in mid-afternoon and because of uneven distribution of soil matric potentials with distance from the roots. Potentials at the root surfaces are lower than in the bulk soil, and once soil water supply starts to limit transpiration, root potentials are substantially less negative in the morning than in the afternoon. This leads to higher stomatal conductances, CO2 assimilation and transpiration in the morning compared to later in the day. Stomatal conductance is sensitive to soil and plant hydraulic properties and to root length density only after approximately 10 d of soil drying, when supply of water by the soil to the roots becomes limiting. High atmospheric demand causes transpiration rates, LE, to decline at a slightly higher soil water content, ,s, than at low atmospheric demand, but all curves of LE versus ,s fall on the same line when soil water supply limits transpiration. Stomatal conductance cannot be modelled in isolation, but must be fully coupled with models of photosynthesis/respiration and the transport of water from soil, through roots, stems and leaves to the atmosphere. [source]

Relations between stomatal closure, leaf turgor and xylem vulnerability in eight tropical dry forest trees

PLANT CELL & ENVIRONMENT, Issue 3 2003
T. J. BRODRIBB
ABSTRACT This study examined the linkage between xylem vulnerability, stomatal response to leaf water potential (,L), and loss of leaf turgor in eight species of seasonally dry tropical forest trees. In order to maximize the potential variation in these traits species that exhibit a range of leaf habits and phenologies were selected. It was found that in all species stomatal conductance was responsive to ,L over a narrow range of water potentials, and that ,L inducing 50% stomatal closure was correlated with both the ,L inducing a 20% loss of xylem hydraulic conductivity and leaf water potential at turgor loss in all species. In contrast, there was no correlation between the water potential causing a 50% loss of conductivity in the stem xylem, and the water potential at stomatal closure (,SC) amongst species. It was concluded that although both leaf and xylem characters are correlated with the response of stomata to ,L, there is considerable flexibility in this linkage. The range of responses is discussed in terms of the differing leaf-loss strategies exhibited by these species. [source]

The Ball,Berry,Leuning and Tardieu,Davies stomatal models: synthesis and extension within a spatially aggregated picture of guard cell function

PLANT CELL & ENVIRONMENT, Issue 11 2002
R. C. Dewar
Abstract A new model of stomatal conductance is proposed which combines the essential features of the Ball,Berry,Leuning (BBL) and Tardieu,Davies (TD) models within a simple spatially aggregated picture of guard cell function. The model thus provides a coherent description of stomatal responses to both air and soil environments. The model also presents some novel features not included in either the BBL or TD models: stomatal sensing of intercellular (rather than leaf surface) CO2 concentration; an explanation of all three observed regimes (A, B and C) of the stomatal response to air humidity (Monteith Plant, Cell and Environment 18, 357,364, 1995); incorporation of xylem embolism; and maintenance of hydraulic homeostasis by combined hydraulic and chemical signalling in leaves (in which leaf epidermal hydraulic conductivity plays a key role). Significantly, maintenance of hydraulic homeostasis in the model does not require a direct feedback signal from xylem embolism, the predicted minimum leaf water potential being independent of xylem hydraulic conductivity. It is suggested that stomatal regulation through combined hydraulic and chemical signalling in leaves and/or roots provides a general mechanism enabling plants to maintain their water potentials above a minimum value. Natural selection of the key stomatal parameters would then set the minimum potential to a specific value determined by the most vulnerable plant process under water stress (e.g. cell growth, protein synthesis or xylem cavitation), depending on species and growth conditions. [source]

Evaluating different soil and plant hydraulic constraints on tree function using a model and sap flow data from ponderosa pine

PLANT CELL & ENVIRONMENT, Issue 7 2001
M. Williams
Relationships between tree size and physiological processes such as transpiration may have important implications for plant and ecosystem function, but as yet are poorly understood. We used a process-based model of the soil,plant,atmosphere continuum to investigate patterns of whole-tree sap flow in ponderosa pine trees of different size and age (36 m and ,250 years versus 13 m and 10,50 years) over a developing summer drought. We examined three different hypothetical controls on hydraulic resistance, and found that size-related differences in sap flow could be best explained by absolute differences in plant resistance related to path length (hypothesis 1) rather than through different dynamic relationships between plant resistance and leaf water potential (hypothesis 2), or alterations in rates of cumulative inducement and repair of cavitation (hypothesis 3). Reductions in sap flow over time could be best explained by rising soil,root resistance (hypothesis 1), rather than by a combination of rising plant and soil,root resistance (hypothesis 2), or by rising plant resistance alone (hypothesis 3). Comparing hourly predictions with observed sap flow, we found that a direct relationship between plant resistance and leaf water potential (hypothesis 2) led to unrealistic bimodal patterns of sap flow within a day. Explaining seasonal reduction in sap flow purely through rising plant resistance (hypothesis 3) was effective but failed to explain the observed decline in pre-dawn leaf water potential for small trees. Thus, hypothesis 1 was best corroborated. A sensitivity analysis revealed a significant difference in the response to drought-relieving rains; precipitation induced a strong recovery in sap flow in the hypothetical case of limiting soil,root resistance (hypothesis 1), and an insignificant response in the case of limiting plant resistance (hypothesis 3). Longer term monitoring and manipulation experiments are thus likely to resolve the uncertainties in hydraulic constraints on plant function. [source]

Does engineering abscisic acid biosynthesis in Nicotiana plumbaginifolia modify stomatal response to drought?

PLANT CELL & ENVIRONMENT, Issue 5 2001
C. Borel
ABSTRACT The consequences of manipulating abscisic acid (ABA) biosynthesis rates on stomatal response to drought were analysed in wild-type, a full-deficient mutant and four under-producing transgenic lines of N. plumbaginifolia. The roles of ABA, xylem sap pH and leaf water potential were investigated under four experimental conditions: feeding detached leaves with varying ABA concentration; injecting exogenous ABA into well-watered plants; and withholding irrigation on pot-grown plants, either intact or grafted onto tobacco. Changes in ABA synthesis abilities among lines did not affect stomatal sensitivity to ABA concentration in the leaf xylem sap ([ABA]xyl), as evidenced with exogenous ABA supplies and natural increases of [ABA]xyl in grafted plants subjected to drought. The ABA-deficient mutant, which is uncultivable under normal evaporative demand, was grafted onto tobacco stock and then presented the same stomatal response to [ABA]xyl as wild-type and other lines. This reinforces the dominant role of ABA in controlling stomatal response to drought in N. plumbaginifolia whereas roles of leaf water potential and xylem sap pH were excluded under all studied conditions. However, when plants were submitted to soil drying onto their own roots, stomatal response to [ABA]xyl slightly differed among lines. It is suggested, consistently with all the results, that an additional root signal of soil drying modulates stomatal response to [ABA]xyl. [source]

Physiological responses of lupin genotypes to terminal drought in a Mediterranean-type environment

ANNALS OF APPLIED BIOLOGY, Issue 3 2007
J.A. Palta
Abstract Field experiments concerning lupin grown in a low-rainfall environment of the Mediterranean climatic region of Western Australia were conducted over three seasons to identify and evaluate the characteristics that maximise yield per unit of rainfall. The characteristics of early flowering and podding, high pod retention, fast rates of seed filling, osmotic adjustment and the degree of dry matter transfer from stem to the seed were studied in 12 lupin genotypes differing in seed yield under conditions of terminal drought. To allow recently released cultivars and advanced breeding lines to be evaluated, five to six genotypes were included in the first and the third year and nine in the second year. The genotypes were grown rainfed until pod set and then under a rainout shelter. Flowering and podding dates, pod retention, seed growth rate and osmotic adjustment were measured in detail, together with leaf water potential, seed yield and its components. The timing and intensity of development of the terminal drought varied from average in 1998 and 1999 to extreme in 2000. In each year, the seed yield under terminal drought showed genotypic differences, which appeared consistent with the timing and intensity of the development of terminal drought. Early flowering and podding were significantly correlated with seed yield. Fast rates of seed growth were highly and significantly correlated with high yields regardless of the intensity of development of terminal drought. Pod retention was highly correlated with yield in seasons in which the intensity of the development of terminal drought was average but not under extreme conditions of terminal drought. This was because the seed number per pod was markedly reduced to compensate for the high number of pods retained. Osmotic adjustment did not occur during the development of terminal drought in any of the genotypes. Dry matter transfer from stems to seeds was insignificant and not related to seed yield, suggesting that it is not a useful characteristic in screening for high yield under terminal drought. [source]

Subtle topographical differences along a floodplain promote different plant strategies among Paspalum dilatatum subspecies and populations

AUSTRAL ECOLOGY, Issue 2 2010
FEDERICO P. O. MOLLARD
Abstract It was hypothesised that subtle topographical differences might cause the existence of ecotypes along a floodplain. The apomict grass Paspalum dilatatum subspecies dilatatum inhabits flood-prone lowlands as well as nearby uplands in the floodplains of Argentina, while the sexual P. dilatatum subspecies flavescens almost exclusively inhabits the uplands. The aim of the present study was to identify the different traits that allow these P. dilatatum populations to inhabit different habitats. Plants of P. dilatatum were reciprocally transplanted between uplands and lowlands. Morphophysiological traits related to flooding tolerance were measured during a flood. Subspecies dilatatum from the uplands and subspecies flavescens showed a high physiological performance in the uplands but a considerable decrease in stomatal conductance, net photosynthesis rates and tiller number in the flooded lowlands. In contrast, the subspecies dilatatum from the lowlands showed relatively lower and stable stomatal conductance, photosynthesis rates and leaf water potential at both sites. Subspecies dilatatum from the lowlands outperformed upland populations at the lowland site with respect to tillering. Leaves of subspecies dilatatum from the lowlands that had grown at the lowland habitat had a lower blade/sheath proportion than leaves of plants transplanted to the uplands. This behavior did not occur in both upland populations. Results suggest that dilatatum Lowland plants have the typical strategy of stress-tolerant genotypes and that the upland populations are adapted to habitats where competitive species are selected. In conclusion, habitats with subtle differences in topographic level can favour both ecotypic differentiations within an apomict subspecies but also the maintenance of morphophysiological similitudes between coexisting upland populations belonging to different subspecies. [source]

Identification and significance of sources of spatial variation in grapevine water status

AUSTRALIAN JOURNAL OF GRAPE AND WINE RESEARCH, Issue 1 2010
J.A. TAYLOR
Abstract Background and Aims:, Water stress in grapevines is directly linked to grape quality. Differential vine water management should therefore be strongly linked to the water stress in the vine. To do this, an understanding of the dominant drivers and indicators of vine water status are needed from a sub-block to whole vineyard level. This understanding will help generate effective vine water status models for variable rate irrigation systems. Methods and Results:, A vineyard in the south of France was sampled for pre-dawn leaf water potential (,PD) at several dates during the growing season for two consecutive years. Sampling was stratified by soil types and relative within-block vegetative expression. A recursive partitioning analysis identified that cultivar had a dominant effect at low water stress, while vegetative expression and then soil unit effects became dominant as water restriction increased. Variance in ,PD was calculated at difference scales (plant, site, block and vineyard) and Smith's heterogeneity law was used to evaluate the scalar nature of ,PD variance. Spatial heterogeneity increased as the season and water restriction increased. Conclusion:, Variance in ,PD changed temporally through a season and the dominant drivers/indicators also changed. The opportunity to spatially manage water stress (irrigation) increased as water restriction increased. Significance of the Study:, Managing vine water stress helps optimise production and a ,PD model would be a useful addition to a viticulture decision support system. This study identified how the variance in ,PD evolved during a season and the best ancillary indicators of ,PD for spatial and temporal modelling. [source]

ABA during reproductive development in non-irrigated grapevines (Vitis vinifera L. cv. Tempranillo)

AUSTRALIAN JOURNAL OF GRAPE AND WINE RESEARCH, Issue 3 2003
M. CARMEN ANTOLÍN
Abstract In grapevines, stomatal aperture decreases after a mid-morning peak during summer days. Afternoon stomatal closure increases in non-irrigated plants as water limitation progresses, which suggests the involvement of abscisic acid (ABA) in the control of stomatal aperture. The objective of this work was to study the seasonal and diurnal time-courses of CO2 assimilation rate, leaf conductance, leaf water potential +, and ABA concentration in xylem sap, leaves, flowers and berries in non-irrigated field-grown Tempranillo grapevines throughout reproductive development. Leaf decreased throughout fruit development because water availability decreased towards the end of the reproductive cycle. CO2 assimilation rate, leaf conductance and xylem ABA concentration also decreased during the course of the growing season. Combining all measurements xylem ABA was either not correlated, or only slightly correlated, with leaf water status + and daily leaf conductance, respectively. This lack of relationship indicates that xylem ABA during fruit ripening had functions other than provision of a non-hydraulic signal. On a seasonal basis, xylem ABA concentration measured in non-irrigated grapevines was well related to berry ABA concentration, especially at the end of fruit development (veraison and harvest). [source]

Defoliation alters water uptake by deep and shallow roots of Prosopis velutina (Velvet Mesquite)

FUNCTIONAL ECOLOGY, Issue 3 2003
K. A. Snyder
Summary 1Prosopis velutina Woot. (Velvet Mesquite) at a site with limited groundwater availability derived a greater percentage of water from shallow soil at the onset of the summer rainy season than did trees at a site with greater availability of groundwater. Predawn leaf water potentials (,pd) were not a strong indicator of shallow water use for this species with roots in multiple soil layers. 2We experimentally defoliated P. velutina plants to determine if reduced-canopy photosynthesis would alter vertical patterns of root activity. After natural rain events, hydrogen isotope ratios of xylem sap indicated that defoliated P. velutina took up a greater percentage of its water from shallow soils than did undefoliated plants. 3Irrigation with deuterium-labelled water further demonstrated that undefoliated plants were able to use shallow soil water. Defoliation appeared to affect the ability of trees to use deep-water sources. 4Reduced carbon assimilation limited water uptake from deep soil layers. These data highlight that there are internal physiological controls on carbon allocation that may limit water uptake from different soil layers. During periods of high vapour pressure deficit or soil drought, when leaf gas exchange and carbon assimilation decline, this may create positive feedbacks where plants are unable to forage for deep water due to carbon limitations. [source]

Photosynthetic Responses of a Temperate Liana to Xylella fastidiosa Infection and Water Stress

JOURNAL OF PHYTOPATHOLOGY, Issue 1 2004
A. J. McElrone
Abstract Xylella fastidiosa is a xylem-limited bacterial plant pathogen that causes bacterial leaf scorch in its hosts. Our previous work showed that water stress enhances leaf scorch symptom severity and progression along the stem of a liana, Parthenocissus quinquefolia, infected by X. fastidiosa. This paper explores the photosynthetic gas exchange responses of P. quinquefolia, with the aim to elucidate mechanisms behind disease expression and its interaction with water stress. We used a 2 × 2-complete factorial design, repeated over two growing seasons, with high and low soil moisture levels and infected and non-infected plants. In both years, low soil moisture levels reduced leaf water potentials, net photosynthesis and stomatal conductance at all leaf positions, while X. fastidiosa -infection reduced these parameters at basally located leaves only. Intercellular CO2 concentrations were reduced in apical leaves, but increased at the most basal leaf location, implicating a non-stomatal reduction of photosynthesis in leaves showing the greatest disease development. This result was supported by measured reductions in photosynthetic rates of basal leaves at high CO2 concentrations, where stomatal limitation was eliminated. Repeated measurements over the summer of 2000 showed that the effects of water stress and infection were progressive over time, reaching their greatest extent in September. By reducing stomatal conductances at moderate levels of water stress, P. quinquefolia maintained relatively high leaf water potentials and delayed the onset of photosynthetic damage due to pathogen and drought-induced water stress. In addition, chlorophyll fluorescence measurements showed that P. quinquefolia has an efficient means of dissipating excess light energy that protects the photosynthetic machinery of leaves from irreversible photoinhibitory damage that may occur during stress-induced stomatal limitation of photosynthesis. However, severe stress induced by disease and drought eventually led to non-stomatal decreases in photosynthesis associated with leaf senescence. [source]

Height-related trends in leaf xylem anatomy and shoot hydraulic characteristics in a tall conifer: safety versus efficiency in water transport

NEW PHYTOLOGIST, Issue 1 2008
D. R. Woodruff
Summary ,,Hydraulic vulnerability of Douglas-fir (Pseudotsuga menziesii) branchlets decreases with height, allowing shoots at greater height to maintain hydraulic conductance (Kshoot) at more negative leaf water potentials (,l). ,,To determine the basis for this trend shoot hydraulic and tracheid anatomical properties of foliage from the tops of Douglas-fir trees were analysed along a height gradient from 5 to 55 m. ,,Values of ,l at which Kshoot was substantially reduced, declined with height by 0.012 Mpa m,1. Maximum Kshoot was reduced by 0.082 mmol m,2 MPa,1 s,1 for every 1 m increase in height. Total tracheid lumen area per needle cross-section, hydraulic mean diameter of leaf tracheid lumens, total number of tracheids per needle cross-section and leaf tracheid length decreased with height by 18.4 µm2 m,1, 0.029 µm m,1, 0.42 m,1 and 5.3 µm m,1, respectively. Tracheid thickness-to-span ratio (tw/b)2 increased with height by 1.04 × 10,3 m,1 and pit number per tracheid decreased with height by 0.07 m,1. ,,Leaf anatomical adjustments that enhanced the ability to cope with vertical gradients of increasing xylem tension were attained at the expense of reduced water transport capacity and efficiency, possibly contributing to height-related decline in growth of Douglas fir. [source]