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In some forest systems, stomata have also been observed to reopen rapidly on recovery from drought, with delays in gas exchange recovery only observed once embolism-induced declines in hydraulic conductance occur ([29]). (B) When relief from a drought occurs after embolism has formed in the xylem then gas exchange recovery can take many months in species that must construct new xylem and organs to regain pre-drought gas exchange capacity ([3], [1]). [2] report that on rewatering from a drought severe enough to close stomata, the complete recovery of leaf gas exchange took >7 days, yet water potentials recovered within 12 h of rewatering. [Extracted from the article]

Clarifying the mechanisms underlying the recovery of gas exchange following drought is the key to providing insights into plant drought adaptation and habitat distribution. However, the mechanisms are still largely unknown. Targeting processes known to inhibit gas exchange during drought recovery, we measured leaf water potential, the leaf hydraulic conductance, stomatal reopening, abscisic acid (ABA) and the ethylene emission rate (EER) following moderate drought stress in seedlings of the globally pervasive woody tree Fraxinus chinensis. We found strong evidence that the slow stomatal reopening after rehydration is regulated by a slow decrease in EER, rather than changes in leaf hydraulics or foliar ABA levels. This was supported by evidence of rapid gas exchange recovery in plants after treatment with the ethylene antagonist 1-methylcyclopropene. These findings provide evidence to rigorously support ethylene as a key factor constraining stomatal reopening from moderate drought directly, thereby potentially opening new windows for understanding species drought adaptation. [ABSTRACT FROM AUTHOR]

The study of ancient species provides valuable information concerning the evolution of specific adaptations to past and current environmental conditions. Araucaria araucana (Molina) K. Koch belongs to one of the oldest families of conifers in the world, but despite this, there are few studies focused on its physiology and responses to changes in environmental conditions. We used an integrated approach aimed at comprehensively characterizing the ecophysiology of this poorly known species, focusing in its stomatal, mesophyll and biochemical traits, hypothesizing that these traits govern the carbon assimilation of A. araucana under past and present levels of atmospheric CO2. Results indicated that A. araucana presents the typical traits of an ancient species, such as large stomata and low stomatal density, which trigger low stomatal conductance and slow stomatal responsiveness to changing environmental conditions. Interestingly, the quantitative analysis showed that photosynthetic rates were equally limited by both diffusive and biochemical components. The Rubisco catalytic properties proved to have a low Rubisco affinity for CO2 and O2, similar to other ancient species. This affinity for CO2, together with the low carboxylation turnover rate, are responsible for the low Rubisco catalytic efficiency of carboxylation. These traits could be the result of the diverse environmental selective pressures that A. araucana was exposed during its diversification. The increase in measured temperatures induced an increase in stomatal and biochemical limitations, which together with a lower Rubisco affinity for CO2 could explain the low photosynthetic capacity of A. araucana in warmer conditions. [ABSTRACT FROM AUTHOR]

Extreme drought is one of the key climatic drivers of tree mortality on a global scale. However, it remains unclear whether the drought-induced tree mortality will increase under nocturnal climate warming. Here we exposed seedlings of two wide-ranging subtropical tree species, Castanopsis sclerophylla and Schima superba , with contrasting stomatal regulation strategies to prolonged drought under ambient and elevated night-time temperature by 2 °C. We quantified the seedling survival time since drought treatment by measuring multiple leaf traits such as leaf gas exchange, predawn leaf water potential and water-use efficiency. The results showed that all seedlings in the ambient temperature died within 180 days and 167 days of drought for C. sclerophylla and S. superba , respectively. Night warming significantly shortened the survival time of C. sclerophylla , by 31 days, and S. superba by 28 days, under the drought treatment. A survival analysis further showed that seedlings under night warming suffered a 1.6 times greater mortality risk than those under ambient temperature. Further analyses revealed that night warming suppressed net leaf carbon gain in both species by increasing the nocturnal respiratory rate of S. superba across the first 120 days of drought and decreasing the photosynthetic rate of both species generally after 46 days of drought. These effects on net carbon gain were more pronounced in S. superba than C. sclerophylla. After 60 days of drought, night warming decreased the predawn leaf water potential and leaf water-use efficiency of C. sclerophylla but not S. superba. These contrasting responses are partially due to variations in stomatal control between the two species. These findings suggest that stomatal traits can regulate the response of leaf gas exchange and plant water-use to nocturnal warming during drought. This study indicates that nocturnal warming can accelerate tree mortality during drought. Night warming accelerates the mortality of two subtropical seedlings under drought. Night warming differently affects the drought response of leaf gas exchange and plant water-use between the two species due to species-specific stomatal morphological traits. Carbon metabolism changes and hydraulic damage play differential roles in driving night-warming impacts on the drought-induced mortality between the two species. [ABSTRACT FROM AUTHOR]

Long-term high CO2 exposure accelerates photosynthetic induction response due to rapid light increase. However, it is unclear whether the acceleration is caused by acclimation of photosynthetic components (long-term CO2 effect) and/or by the sufficient substrate under high CO2 at the measurement (short-term CO2 effect). Populus koreana × trichocarpa cv. Peace has wide-open stomata almost not responding to changes of photon flux density. Using this species, we examined the long- and short-term CO2 effects on photosynthetic induction by focusing on biochemical components. We grew the plants under [CO2] of 380, 700 and 1020 μmol CO2 mol−1 air and measured the photosynthetic induction response under [CO2] of 380 and 1020 μmol CO2 mol−1 air. Despite significant reduction in Rubisco content and light-saturated photosynthetic rate in the leaves from the high growth CO2, the photosynthetic induction time was similar in leaves from different growth CO2 plants when measurement [CO2] was the same. The induction, however, was significantly fast at the higher than at the lower measurement [CO2], regardless of growth CO2 of the plants. These results demonstrate that the acceleration of apparent photosynthetic induction under high CO2 environment was mainly contributed by a short-term CO2 effect rather than by a long-term acclimation effect when stomatal limitation is not the major factor. [ABSTRACT FROM AUTHOR]

The occurrence of amphistomatic leaves (stomata on both surfaces) versus hypostomatic leaves (stomata limited to the lower or abaxial surface) has strong associations with environment. Amphistomy provides the advantage of higher conductance of CO2 for photosynthesis, however, unless the stomata on both leaf surfaces can be independently controlled in response to environmental cues, amphistomy may lead to inefficient gas exchange. While previous studies have found evidence that stomata can operate independently across and between surfaces of dorsiventral leaves, we investigate whether an independent stomatal response can be induced for isobilateral leaves by largely natural conditions. Here, we exposed surfaces of isobilateral, amphistomatic Eucalyptus globulus Labill. leaves to natural diurnal variation in differential evaporative demand, using leaf orientation to drive differences in irradiance and heat load on leaf surfaces. We identified preferential closure of stomata on the surface exposed to higher irradiation (and therefore evaporative demand) during the afternoon under natural conditions and similarly induced differential stomatal closure under experimental conditions in the laboratory. The differential response confirms that sufficient hydraulic isolation exists for independent stomatal response to occur between surfaces of amphistomatic, isobilateral leaves, and importantly, we show that natural conditions can induce surface-specific stomatal closure. [ABSTRACT FROM AUTHOR]

Plant surface properties influence solid-liquid interactions and matter exchange between the organs and their surrounding environment. In the case of fruits, surface processes may be of relevance for seed production and dispersal. To gain insight into the relationship between surface structure, chemical composition and function of aerial reproductive organs, we performed diverse experiments with the dry, winged fruits, or samaras, of Ulmus laevis Pall. and Ulmus minor Mill. both at the time of full maturity (green samaras) and of samara dispersal (dry samaras). Samaras of both elm species showed positive photosynthetic rates and absorbed water through their epidermal surfaces. The surface wettability, free energy, polarity and solubility parameter were lower in U. laevis than in U. minor and decreased for dry samaras in both species. Ulmus laevis samaras had a high degree of surface nano-roughness mainly conferred by cell wall folds containing pectins that substantially increased after hydration. The samaras in this species also had a thicker cuticle that could be isolated by enzymatic digestion, whereas that of U. minor samaras had higher amounts of soluble lipids. Dry samaras of U. laevis had higher floatability and lower air sustentation than those of U. minor. We concluded that samaras contribute to seed development by participating in carbon and water exchange. This may be especially important for U. minor, whose samaras develop before leaf emergence. The trichomes present along U. laevis samara margin may enhance water absorption and samara floatability even in turbulent waters. In general, U. minor samaras show traits that are consistent with a more drought tolerant character than U. laevis samaras, in line with the resources available both at the tree and ecosystem level for these species. Samara features may additionally reflect different adaptive strategies for seed dispersal and niche differentiation between species, by favoring hydrochory for U. laevis and anemochory for U. minor. [ABSTRACT FROM AUTHOR]

Clonal integration between ramets can be an ecological advantage of clonal plant species in environments where resources are patchily distributed. We investigated physiological integration among Populus balsamifera L. ramets under drought stress in order to demonstrate water sharing between connected ramets. Pairs of connected ramets were grown in separate pots in the greenhouse where half of ramets had the parental root connection severed and half were left intact. Drought stress was applied to one ramet, and growth, specific leaf area (SLA), net photosynthesis, stomatal conductance, leaf water potential and carbon isotopic composition (δ13C) were measured after an 8-week growing period. Droughted ramets connected to watered ramets were able to maintain high gas exchange activity and water potential, similar to watered ramets. Leaf water potential and SLA results showed that the root connection was more beneficial for proximal compared with distal ramets. The parental root connection also allowed droughted ramets to discriminate more against 13C compared with severed ramets. In conclusion, this study shows compelling evidence of physiological integration of connected P. balsamifera ramets through water sharing. [ABSTRACT FROM AUTHOR]

In this article the author discusses patterns of stomatal conductance in response to long-term environmental changes. The author states that the models of stomatal conductance based on the old concepts of multiplicative constraints and semi-mechanistic parameterizations. The author further discusses the Bayesian Hierarchical model of stomatal conductance and two measurement patterns of estimating stomatal conductance including gas exchange and sap flux.

Patchy stomatal closure occurs in plants with heterobaric leaves, in which vertical extensions of bundle sheath cells delimit the mesophyll and restrict the diffusion of CO2. The scale of patchy stomatal behavior was investigated in this study. The distribution of PSII quantum yield (ΦII) obtained from chlorophyll fluorescence images was used to evaluate the scale of stomatal patchiness and its relationship with leaf photosynthesis in the sun leaves of 2-year-old saplings of Quercus crispula Blume. Fluorescent patches were observed only during the day with low stomatal conductance. Comparison of numerical simulation of leaf gas exchange and chlorophyll fluorescence images showed that heterogeneous distribution of electron transport rate through PSII (J) was observed following stomatal closure with a bimodal manner under both natural and saturated photosynthetic photon flux densities. Thus, fluorescence patterns can be interpreted in terms of patchy stomatal closure. The mapping of J from chlorophyll fluorescence images showed that the scale of stomatal patchiness was approximately 2.5-fold larger than that of anatomical patches (lamina areas bounded by bundle sheath extensions within lamina). Our results suggest the spatial scale of stomatal patches in Q. crispula leaves. [ABSTRACT FROM AUTHOR]

Trees adapted to mesic and xeric habits may differ in a suite of physiological responses that affect leaf-level carbon balance, including the relationship between photosynthesis (A) and respiration at night (Rn). Understanding the factors that regulate physiological function in mesic and xeric species is critical for predicting changes in growth and distribution under changing climates. In this study, we examined the relationship between A and Rn, and leaf traits that may regulate A and Rn, in six Eucalyptus species native to mesic or xeric ecosystems, during two 24-h cycles in a common garden under high soil moisture. Peak A and Rn generally were higher in xeric compared with mesic species. Across species, A and Rn covaried, correlated with leaf mass per area, leaf N per unit area and daytime soluble sugar accumulation. A also covaried with gs, which accounted for 93% of the variation in A within species. These results suggest that A and Rn in these six Eucalyptus species were linked through leaf N and carbohydrates. Further, the relationship between A and Rn across species suggests that differences in this relationship between mesic and xeric Eucalyptus species in their native habitats may be largely driven by environmental factors rather than inter-specific genetic variation. [ABSTRACT FROM AUTHOR]

A conceptual model was tested for explaining environmental and physiological effects on leaf gas exchange in the deciduous dry tropical woodland tree Boswellia papyrifera (Del.) Hochst. For this species we aimed at (i) understanding diurnal patterns in leaf gas exchange, (ii) exploring cause–effect relationships among external environment, internal physiology and leaf gas exchange, and (iii) exploring site differences in leaf gas exchange in response to environmental variables. Diurnal courses in gas exchange, underlying physiological traits and environmental variables were measured for 90 trees on consecutive days at two contrasting areas, one at high and the other at low altitude. Assimilation was highest in the morning and slightly decreased during the day. In contrast, transpiration increased from early morning to midday, mainly in response to an increasing vapor pressure deficit (VPD) and gradual stomatal closure. The leaf water potential varied relatively little and did not influence gas exchange during the measurement period. Our results suggest that the same cause–effect relationships function at contrasting areas. However, leaves at the higher altitude had higher photosynthetic capacity, reflecting acclimation to higher light levels. Trees at both areas nevertheless achieved similar leaf assimilation rates since assimilation was down-regulated by stomatal closure due to the higher VPD at the higher altitude, while it became more light limited at the lower altitude. Gas exchange was thus limited by a high VPD or low light levels during the wet season, despite the ability of the species to acclimate to different conditions. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate, during the summer of the year 2008, the variation in leaf water and photosynthetic characteristics of Eucryphia cordifolia Cav. (Cunoniaceae) along its broad latitudinal distribution in central south Chile (36° to 42° S). The latitudinal variation in water potential (Ψw), water potential at saturation (Ψπsat), water potential at the turgor lost point (Ψπtlp), stomatal density of the leaves, leaf nitrogen concentrations and photosynthetic light response were studied in eight populations. The populations located in the northern region of the distribution of E. cordifolia had the lowest leaf water potential. Osmotic potential at full turgor was highest in the two southernmost populations and gradually decreased towards the northernmost points. Similarly, osmotic potential at zero turgor was the lowest in the northern population. On the contrary, the symplastic water content was lower in the two southernmost populations. The highest net photosynthesis rate was recorded for plants in the populations of intermediate distributions, and it was dependent on the precipitation and temperature gradient. The northern populations, which are subject to the lowest precipitations, showed the lowest stomatal densities, which were tightly linked with stomatal conductance variation. Therefore, the variability of Amax was independent of stomatal density and conductance, so that the northern populations, subject to environments with less water availability, presented higher photosynthetic water use efficiency. Photosynthesis variations were also not associated with changes in leaf water potential or in nitrogen content in E. cordifolia leaves, which did not show any consistent latitudinal or altitudinal trend. In conclusion, the results support our hypothesis that the leaf water relations, stomatal characteristics and photosynthetic rates of the leaf would vary along its latitudinal gradient, helping to explain the ability of E. cordifolia trees to inhabit a broad latitudinal and altitudinal range throughout the central south Chile. [ABSTRACT FROM AUTHOR]

Foliar gas exchange and carbon (δ13C) and oxygen (δ18O) isotope ratios were measured in a young blackbutt (Eucalyptus pilularis Sm.) plantation subjected to four weed control treatments defined by the width of the weed-free strip maintained for the first 12 months after planting. Treatments were: 2-m-wide weed-free strip (50% of plot area, 2.0MWC), 1.5-m-wide weed-free strip (37.5% of plot area, 1.5MWC), 1-m-wide weed-free strip (25% of plot area, 1.0MWC) and no weed control (NWC). Our objectives were to determine (1) if decreasing the width of the weed control strip (decreasing herbicide use) affected growth and leaf photosynthesis of the plantation, and (2) the effects of the weed control regimes on variations in relative stomatal and biochemical limitations to photosynthesis. Trees in the 1.0MWC treatment had lower foliar light-saturated photosynthetic rate (Asat) than trees in the 2.0MWC treatment. An increase in metabolic limitation was responsible for the decrease in Asat in the 1.0MWC trees, which was also partly confirmed by the isotopic data. Compared with trees in the 1.0MWC, 1.5MWC and 2.0MWC treatments, Asat of NWC trees was significantly lower, a difference that was attributable mainly to stomatal limitation and to a lesser extent to biochemical limitation. The results support the conclusion that different weed control regimes cause differences in relative stomatal and biochemical limitations to plantation photosynthesis. This report contributes to a growing body of literature on competition for soil resources between trees and weeds. Our results highlight the usefulness of the stable isotopic method in supporting analysis of the response of net photosynthesis to varying intercellular CO2 concentration for determining the relative stomatal and non-stomatal limitations to photosynthesis under experimental conditions in the field. [ABSTRACT FROM AUTHOR]

Seasonal patterns of cytokinins (CKs) and microclimate were examined in the upper, middle and lower canopy layers of mature Acer saccharum Marsh. (sugar maple) trees to elucidate the potential role of CKs in the mediation of gas exchange. The upper canopy showed a distinctly dissimilar microclimate from the middle and lower canopy layers with higher photosynthetically active radiation and wind speed, but showed no corresponding differences in transpiration (E) or stomatal conductance (gs). Although E and gs tended to be higher in the upper canopy than in the middle and lower canopies, the differences were not significant, indicating regulation beyond the passive response to changes in microclimate. The upper canopy accumulated significantly higher concentrations of CKs, predominantly as ribosides, and all canopy layers showed distinct seasonal patterns in CK profiles. Multiple regression models showed significant relationships between both gs and E and foliar CK concentration, although these relationships varied among canopy layers. The relationships were strongest in the middle and lower canopy layers where there was less fluctuation in leaf water status and less variability in abiotic variables. The relationships between gas exchange parameters and leaf CK concentration began to decouple near the end of the growing season as foliar phytohormone concentrations changed with the approach of dormancy. [ABSTRACT FROM AUTHOR]

This study examined relationships between foliar morphology and gas exchange characteristics as they vary with height within and among crowns of Sequoia sempervirens D. Don trees ranging from 29 to 113 m in height. Shoot mass:area (SMA) ratio increased with height and was less responsive to changes in light availability as height increased, suggesting a transition from light to water relations as the primary determinant of morphology with increasing height. Mass-based rates of maximum photosynthesis (Amax,m), standardized photosynthesis (Astd,m) and internal CO2 conductance (gi,m) decreased with height and SMA, while the light compensation point, light saturation point, and mass and area-based rates of dark respiration (Rm) increased with height and SMA. Among foliage from different heights, much of the variation in standardized photosynthesis was explained by variation in gi, consistent with increasing limitation of photosynthesis by internal conductance in foliage with higher SMA. The syndrome of lower internal and stomatal conductance to CO2 and higher respiration may contribute to reductions in upper crown growth efficiency with increasing height in S. sempervirens trees. [ABSTRACT FROM AUTHOR]