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Cortical lacunae caused by drought, especially observed in hybrids originating from Vitis rupestris, disrupt the connection between roots and soil. Yet, the physiological processes behind lacuna formation during drought and its consistency across Vitis species remain unclear. Here, we used a root pressure probe to investigate fine root hydraulic and mechanical properties, in the arid‐adapted R‐65 and drought‐susceptible 101‐14Mgt cultivars. We then performed P–V curves, root sap osmolality, and electrolyte leakage (EL) and used fluorescent light microscopy techniques. Only 101‐14Mgt showed lacunae formation during drought due to its stiffer cortical tissue, unlike R‐65. Lacunae resulted in a notable decline in root hydraulic conductivity during severe drought, with increased EL and root sap osmolality, indicating potential cellular damage. R‐65 displayed different and xerophyte‐like characteristics featuring a higher turgor loss point and decreased root capacitance, essential for maintaining root structural integrity in arid conditions. Our findings highlight lacuna formation is impacted by root tissue elasticity possibly linked to specific Vitis species favoring deeper rooting. In arid‐adapted grapevines, hydraulic regulators such as reduced turgor loss point, and root capacitance could contribute to enhanced drought tolerance. [ABSTRACT FROM AUTHOR]

Quantifying drought tolerance in crops is critical for agriculture management under environmental change, and drought response traits in grape vine have long been the focus of viticultural research. Turgor loss point (πtlp) is gaining attention as an indicator of drought tolerance in plants, though estimating πtlp often requires the construction and analysis of pressure-volume (P-V) curves which are very time consuming. While P-V curves remain a valuable tool for assessing πtlp and related traits, there is considerable interest in developing high-throughput methods for rapidly estimating πtlp, especially in the context of crop screening. We tested the ability of a dewpoint hygrometer to quantify variation in πtlp across and within 12 clones of grape vine (Vitis vinifera subsp. vinifera) and one wild relative (Vitis riparia), and compared these results to those derived from P-V curves. At the leaf-level, methodology explained only 4–5% of the variation in πtlp while clone/species identity accounted for 39% of the variation, indicating that both methods are sensitive to detecting intraspecific πtlp variation in grape vine. Also at the leaf level, πtlp measured using a dewpoint hygrometer approximated πtlp values (r2 = 0.254) and conserved πtlp rankings from P-V curves (Spearman's ρ = 0.459). While the leaf-level datasets differed statistically from one another (paired t-test p = 0.01), average difference in πtlp for a given pair of leaves was small (0.1 ± 0.2 MPa (s.d.)). At the species/clone level, estimates of πtlp measured by the two methods were also statistically correlated (r2 = 0.304), did not deviate statistically from a 1:1 relationship, and conserved πtlp rankings across clones (Spearman's ρ = 0.692). The dewpoint hygrometer (taking ∼ 10–15 min on average per measurement) captures fine-scale intraspecific variation in πtlp, with results that approximate those from P-V curves (taking 2–3 h on average per measurement). The dewpoint hygrometer represents a viable method for rapidly estimating intraspecific variation in πtlp, and potentially greatly increasing replication when estimating this drought tolerance trait in grape vine and other crops. [ABSTRACT FROM AUTHOR]

Background and Aims Many agricultural areas are expected to face hotter, drier conditions from climate change. Understanding the mechanisms that crops use to mitigate these stresses can guide breeding for more tolerant plant material. We tested relationships between traits, physiological function in hot conditions and historical climate associations to evaluate these mechanisms for winegrapes. We expected a more negative leaf osmotic potential at full hydration (π o), which reduces leaf turgor loss during drought, and either a metabolically cheaper or more osmoprotectant leaf chemical composition, to allow cultivars associated with hot, dry regions to maintain greater gas exchange in hot growing conditions. Methods We measured π o, gas exchange and leaf chemistry for seven commercially important winegrape cultivars that vary widely in historical climate associations. Vines were grown in common-garden field conditions in a hot wine-growing region (Davis, CA, USA) and measured over the hottest period of the growing season (July–September). Key Results The value of π o varied significantly between cultivars, and all cultivars significantly reduced π o (osmotically adjusted) over the study period, although osmotic adjustment did not vary across cultivars. The value of π o was correlated with gas exchange and climate associations, but in the direction opposite to expected. Photosynthesis and π o were higher in the cultivars associated with hotter, less humid regions. Leaf chemical composition varied between cultivars but was not related to climate associations. Conclusions These findings suggest that maintenance of leaf turgor is not a primary limitation on grapevine adaptation to hot or atmospherically dry growing conditions. Thus, selecting for a more negative π o or greater osmotic adjustment is not a promising strategy to develop more climate-resilient grape varieties, contrary to findings for other crops. Future work is needed to identify the mechanisms increasing photosynthesis in the cultivars associated with hot, dry regions. [ABSTRACT FROM AUTHOR]

As climate change thrives, and the frequency of intense droughts is affecting many forested regions, a mechanistic understanding of the factors conferring drought tolerance in trees is increasingly important. However, studies linking the observed growth reduction to mechanistic traits are still rare. We compared the median growth anomalies of 16 native tree species, gathered across a network of study plots in Bavaria, with the mean species‐specific turgor loss point (πtlp) measured at five locations in Central Europe πtlp explained 37% of the growth anomalies observed in response to the intense droughts between 2018 and 2020 compared to the pre‐drought period between 2006 and 2017 across sites. πtlp constitutes an important leaf drought tolerance trait and influences the growth response of native tree species during extraordinary dry periods. As climate change‐induced droughts intensify, tree species with drought‐tolerant leaves will be less vulnerable to growth reductions. πtlp provides a useful indicator for selecting tree species to adapt forest management systems to climate change. [ABSTRACT FROM AUTHOR]

Summary: Turgor loss point (TLP) is an important proxy for plant drought tolerance, species habitat suitability, and drought‐induced plant mortality risk. Thus, TLP serves as a critical tool for evaluating climate change impacts on plants, making it imperative to develop high‐throughput and in situ methods to measure TLP.We developed hyperspectral pressure–volume curves (PV curves) to estimate TLP using leaf spectral reflectance. We used partial least square regression models to estimate water potential (Ψ) and relative water content (RWC) for two species, Frangula caroliniana and Magnolia grandiflora. RWC and Ψ's model for each species had R2 ≥ 0.7 and %RMSE = 7–10. We constructed PV curves with model estimates and compared the accuracy of directly measured and spectra‐predicted TLP.Our findings indicate that leaf spectral measurements are an alternative method for estimating TLP. F. caroliniana TLP's values were −1.62 ± 0.15 (means ± SD) and −1.62 ± 0.34 MPa for observed and reflectance predicted, respectively (P > 0.05), while M. grandiflora were −1.78 ± 0.34 and −1.66 ± 0.41 MPa (P > 0.05).The estimation of TLP through leaf reflectance‐based PV curves opens a broad range of possibilities for future research aimed at understanding and monitoring plant water relations on a large scale with spectral ecophysiology. [ABSTRACT FROM AUTHOR]

As heatwave frequency increases, they are more likely to coincide with other disturbances like insect defoliation. But it is unclear if high temperatures after defoliation impact canopy recovery or leaf traits which may affect response to further stressors like drought. To examine these stressor interactions, we subjected defoliated (DEF) and undefoliated (UNDEF) oak saplings to a simulated spring heatwave of +10°C for 25 days. We measured gas exchange, leaf area recovery, carbohydrate storage, turgor loss point (ΨTLP), and minimum leaf conductance (gmin). During the heatwave, stem respiration exhibited stronger thermal acclimation in DEF than UNDEF saplings, while stomatal conductance and net photosynthesis increased. The heatwave did not affect leaf area recovery or carbohydrate storage of DEF saplings, but reflush leaves had higher gmin than UNDEF leaves, and this was amplified by the heatwave. Across all treatments, higher gmin was associated with higher daytime stomatal conductance and a lower ΨTLP. The results suggest defoliation stress may not be exacerbated by higher temperatures. However, reflush leaves are less conservative in their water use, limiting their ability to minimise water loss. While lower ΨTLP could help DEF trees maintain gas exchange under mild drought, they may be more vulnerable to dehydration under severe drought. Summary Statement: Leaf area recovery and carbohydrate storage after spring defoliation were not impacted by a coinciding heatwave. However, reflush leaves had higher minimum rates of water loss—and this effect was exacerbated by the heatwave, suggesting reduced drought tolerance. [ABSTRACT FROM AUTHOR]

For wheat (Triticum aestivum), sustained crop yield at limited soil water availability has been linked to osmotic adjustment (OA) – a physiological mechanism that aids maintenance of leaf hydration status, turgor (P) and growth. 'Canada Western Red Spring' (CWRS) wheat cultivars are typically grown in rainfed areas with milder climates, but ongoing climate change is increasesing the frequency and intensity of drought events. The overarching goal of this study was to elucidate if commercially used CWRS cultivars ('Superb', 'Stettler', 'AAC Viewfield') have the ability for leaf OA. Measurements of leaf water relation parameters (water potential, Ψ ; solute potential, Ψ s; stomatal conductance, g s; relative water content, RWC) showed that all three cultivars reached zero P (= Ψ – Ψ s) at a leaf Ψ of −1.1 MPa. Prior to that, P maintenance in 'Superb' and 'AAC Viewfield' was associated with a significant reduction in leaf Ψ s and OA contributed 0.53 MPa ('Superb') and 0.73 MPa ('AAC Viewfield'). Our data analyses provided no support for the existence of OA in 'Stettler'. Under water deficit, leaf g s was significantly higher in 'AAC Viewfield' compared to 'Stettler'; it was intermediate in 'Superb'. Together, drought tolerance in CWRS wheat cultivars is most likely linked to the degree of OA. 'Canada Western Red Spring' wheat cultivars are typically grown in rainfed areas with milder climates, but drought is increasing with climate change. Wheat can maintain yield under dry conditions through the physiological mechanism of osmotic adjustment. We show that two of three studied cultivars of 'Canada Western Red Spring' are capable of osmotic adjustment, permitting a degree of drought tolerance. [ABSTRACT FROM AUTHOR]

The regulation of water loss and the spread of xylem embolism have mostly been considered separately. The development of an integrated approach taking into account the temporal dynamics and relative contributions of these mechanisms to plant drought responses is urgently needed. Do conifer species native to mesic and xeric environments display different hydraulic strategies and temporal sequences under drought? A dry-down experiment was performed on seedlings of four conifer species differing in embolism resistance, from drought-sensitive to extremely drought-resistant species. A set of traits related to drought survival was measured, including turgor loss point, stomatal closure, minimum leaf conductance, and xylem embolism resistance. All species reached full stomatal closure before the onset of embolism, with all but the most drought-sensitive species presenting large stomatal safety margins, demonstrating that highly drought-resistant species do not keep their stomata open under drought conditions. Plant dry-down time to death was significantly influenced by the xylem embolism threshold, stomatal safety margin, and minimum leaf conductance, and was best explained by the newly introduced stomatal margin retention index (SMRIΨ50) which reflects the time required to cross the stomatal safety margin. The SMRIΨ50 may become a key tool for the characterization of interspecific drought survival variability in trees. [ABSTRACT FROM AUTHOR]

Succulence describes the amount of water stored in cells or organs, regardless of plant life-form, including woody and herbaceous plants. In dry environments, plants with greater survival often have greater leaf succulence. However, it is unclear how leaf succulence relates to plant drought resistance strategies, including isohydry (closing stomata to maintain leaf water status) and anisohydry (adjusting cell turgor to tolerate low leaf water status), which exist on a continuum that can be quantified by hydroscape area (larger hydroscape area indicates more anisohydric). We evaluated 12 woody species with differing leaf succulence in a glasshouse dry-down experiment to determine relationships among leaf succulence (degree of leaf succulence, leaf succulent quotient and leaf thickness) and plant drought response (hydroscape area, plant water use, turgor loss point and predawn leaf water potential when transpiration ceased). Hydroscape areas ranged from 0.72 (Carpobrotus modestus S.T.Blake; crassulacean acid metabolism (CAM) plants) to 7.01 MPa2 (Rhagodia spinescens R.Br.; C3 plants), suggesting that C. modestus was more isohydric and R. spinescens was more anisohydric. More isohydric species C. modestus , Carpobrotus rossii (Haw.) Schwantes and Disphyma crassifolium (L.) L.Bolus (CAM plants) had greater leaf succulence, lower root allocation, used stored water and ceased transpiration at higher predawn leaf water potential, shortly after reaching their turgor loss point. The remaining nine species that are not CAM plants had larger hydroscape areas and ceased transpiration at lower predawn leaf water potential. Greater leaf succulence was not related to cumulative water loss until transpiration ceased in drying soils. All 12 species had high turgor loss points (−1.32 to −0.59 MPa), but turgor loss point was not related to hydroscape area or leaf succulence. Our data suggest that overall greater leaf succulence was related to isohydry, but this may have been influenced by the fact that these species were also CAM plants. [ABSTRACT FROM AUTHOR]

Allopolyploidy is a common speciation mechanism in plants; however, its physiological and ecological consequences in niche partitioning have been scarcely studied. In this sense, leaf traits are good proxies to study the adaptive capacity of allopolyploids and diploid parents to their respective environmental conditions. In the present work, leaf water relations (assessed through pressure–volume curves) and structural and anatomical traits of the allotetraploid fern Oeosporangium tinaei and its diploid parents, Oeosporangium hispanicum and Oeosporangium pteridioides, were studied under controlled conditions in response to a water stress (WS) cycle. O. hispanicum showed the lowest osmotic potential at turgor loss point (πtlp) and leaf capacitance, together with higher leaf mass per area (LMA), leaf thickness (LT), leaf density (LD), and leaf dry matter content (LDMC), whereas O. pteridioides presented the opposite set of traits (high πtlp and capacitance, and low LMA, LT, LD, and LDMC). O. tinaei showed an intermediate position for most of the studied traits. The responsiveness (osmotic and elastic adjustments) to WS was low, although most of the traits explained the segregation of the three species across a range of drought tolerance according to the rank: O. hispanicum > O. tinaei > O. pteridioides. These trait differences may underlie the niche segregation among coexisting populations of the three species in the Mediterranean basin. [ABSTRACT FROM AUTHOR]

Leaf hydraulic traits characterize plant drought tolerance and responses to climate change. Yet, plant hydraulics are biased towards northern hemisphere woody species. We collected rhizomes of several perennial grass species along a precipitation gradient in eastern Australia and grew them in an experimental pot study to investigate potential trade‐offs between drought tolerance and plant morphology.We measured the following leaf hydraulic traits: the leaf water potential (Ψleaf) at 50% and 88% loss of leaf hydraulic conductance (P50Kleaf and P88Kleaf), the Ψleaf at 50% loss of stomatal conductance (P50gs), leaf turgor loss point (TLP), leaf dry matter content (LDMC), leaf modulus of elasticity (ε), and the slope of the relationship between predawn and midday Ψleaf. We also measured basal area, tiller density, seed head density, root collar diameter, plant height, and aboveground biomass of each individual.As expected, grass species varied widely in leaf‐level drought tolerance, with loss of 88% hydraulic conductance occurring at a Ψleaf ranging from −1.52 to −4.01 MPa. However, all but one species lost leaf turgor, and most reached P50gs before this critical threshold. Taller more productive grass species tended to have drought vulnerable leaves characterized by low LDMC and less negative P88Kleaf. Species with greater tiller production experienced stomatal closure and lost turgor at more negative Ψleaf. Although our sample size was limited, we found no relationships between these species' traits and their climate of origin.Overall, we identified important hydraulic and morphological trade‐offs in Australian grasses that were surprisingly similar to those observed for woody plants: (1) xylem of taller species was less drought tolerant and (2) turgor loss occurs and stomatal closure begins before significant loss of Kleaf. These data build upon a small yet growing field of grass hydraulics and may be informative of species responses to further drought intensification in Australia. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

The sequence of physiological events during drought strongly impacts plants' overall performance. Here, we synthesized the global data of stomatal and hydraulic traits in leaves and stems of 202 woody species to evaluate variations in the water potentials for key physiological events and their sequence along the climatic gradient. We found that the seasonal minimum water potential, turgor loss point, stomatal closure point, and leaf and stem xylem vulnerability to embolism were intercorrelated and decreased with aridity, indicating that water stress drives trait co‐selection. In xeric regions, the seasonal minimum water potential occurred at lower water potential than turgor loss point, and the subsequent stomatal closure delayed embolism formation. In mesic regions, however, the seasonal minimum water potential did not pose a threat to the physiological functions, and stomatal closure occurred even at slightly more negative water potential than embolism. Our study demonstrates that the sequence of water potentials for physiological dysfunctions of woody plants varies with aridity, that is, xeric species adopt a more conservative sequence to prevent severe tissue damage through tighter stomatal regulation (isohydric strategy) and higher embolism resistance, while mesic species adopt a riskier sequence via looser stomatal regulation (anisohydric strategy) to maximize carbon uptake at the cost of hydraulic safety. Integrating both aridity‐dependent sequence of water potentials for physiological dysfunctions and gap between these key traits into the hydraulic framework of process‐based vegetation models would improve the prediction of woody plants' responses to drought under global climate change. [ABSTRACT FROM AUTHOR]

Summary: Evolutionary relationships are likely to play a significant role in shaping plant physiological and structural traits observed in contemporary taxa. We review research on phylogenetic signal and correlated evolution in plant–water relation traits, which play important roles in allowing plants to acquire, use, and conserve water. We found more evidence for a phylogenetic signal in structural traits (e.g. stomatal length and stomatal density) than in physiological traits (e.g. stomatal conductance and water potential at turgor loss). Although water potential at turgor loss is the most‐studied plant–water relation trait in an evolutionary context, it is the only trait consistently found to not have a phylogenetic signal. Correlated evolution was common among traits related to water movement efficiency and hydraulic safety in both leaves and stems. We conclude that evidence for phylogenetic signal varies depending on: the methodology used for its determination, that is, model‐based approaches to determine phylogenetic signal such as Blomberg's K or Pagel's λ vs statistical approaches such as ANOVAs with taxonomic classification as a factor; on the number of taxa studied (size of the phylogeny); and the setting in which plants grow (field vs common garden). More explicitly and consistently considering the role of evolutionary relationships in shaping plant ecophysiology could improve our understanding of how traits compare among species, how traits are coordinated with one another, and how traits vary with the environment. [ABSTRACT FROM AUTHOR]

Predicting the consequences of climate change is of utmost importance to mitigate impacts on vulnerable ecosystems; plant hydraulic traits are particularly useful proxies for predicting functional disruptions potentially occurring in the near future. This study assessed the current and future regional patterns of leaf water potential at turgor loss point (Ψtlp) by measuring and projecting the Ψtlp of 166 vascular plant species (159 angiosperms and 7 gymnosperms) across a large climatic range spanning from alpine to Mediterranean areas in NE Italy. For angiosperms, random forest models predicted a consistent shift toward more negative values in low‐elevation areas, whereas for gymnosperms the pattern was more variable, particularly in the alpine sector (i.e., Alps and Prealps). Simulations were also developed to evaluate the number of threatened species under two Ψtlp plasticity scenarios (low vs. high plasticity), and it was found that in the worst‐case scenario approximately 72% of the angiosperm species and 68% of gymnosperms within a location were at risk to exceed their physiological plasticity. The different responses to climate change by specific clades might produce reassembly in natural communities, undermining the resilience of natural ecosystems to climate change. [ABSTRACT FROM AUTHOR]

The isohydric–anisohydric continuum describes the relative stringency of stomatal control of leaf water potential (ψleaf) during drought. Hydroscape area (HA)—the water potential landscape over which stomata regulate ψleaf—has emerged as a useful metric of the iso/anisohydric continuum because it is strongly linked to several hydraulic, photosynthetic and structural traits. Previous research on HA focused on broad ecological patterns involving several plant clades. Here we investigate the relationships between HA and climatic conditions and functional traits across ecologically diverse but closely related species while accounting for phylogeny. Across a macroclimatic moisture gradient, defined by the ratio of mean annual precipitation to mean annual pan evaporation (P/Ep), HA decreased with increased P/Ep across 10 Eucalyptus species. Greater anisohydry reflects lower turgor loss points and greater hydraulic safety, mirroring global patterns. Larger HA coincides with mesophyll photosynthetic capacity that is more sensitive to ψleaf. Hydroscapes exhibit little plasticity in response to variation in water supply, and the extent of plasticity does not vary with P/Ep of native habitats. These findings strengthen the case that HA is a useful metric for characterizing drought tolerance and water‐status regulation. Smaller hydroscape area (increased isohydry) in Eucalyptus species is tied to moister climates and drought‐sensitive functional traits like higher turgor loss points and mesophyll photosynthetic sensitivity to leaf water potential. Hydroscape area shows little plasticity to water availability. [ABSTRACT FROM AUTHOR]

Ongoing changes in climate, and the consequent mortality of natural and cultivated forests across the globe, highlight the urgent need to understand the plant traits associated with greater tolerance to drought. Here, we aimed at assessing key foliar traits, with a focus on the hydraulic component, that could confer a differential ability to tolerate drought in three commercial hybrids of the most important Eucalyptus species utilized in tropical silviculture: E. urophyla , E. grandis and E. camaldulensis. All genotypes exhibited similar water potential when the 90% stomatal closure (Ψ g s90) occurs with Ψ g s90 always preceding the start of embolism events. The drought-tolerant hybrid showed a higher leaf resistance to embolism, but the leaf hydraulic efficiency was similar among all genotypes. Other traits presented by the drought-tolerant hybrid were a higher cell wall reinforcement, lower value of osmotic potential at full turgor and greater bulk modulus of elasticity. We also identified that the leaf capacitance after the turgor loss, the ratio between cell wall thickness (t) and lumen breadth (b) ratio (t / b)3, and the minimal conductance might be good proxies for screening drought-tolerant Eucalyptus genotypes. Our findings suggest that xylem resistance to embolism can be an important component of drought tolerance in Eucalyptus in addition to other traits aimed at delaying the development of high tensions in the xylem. Highlight Drought tolerance in tropical Eucalyptus hybrids encompasses a high leaf resistance to embolism and a suite of traits aimed at delaying the development of high tensions in the xylem. [ABSTRACT FROM AUTHOR]

Increasing temperature and drought can result in leaf dehydration and defoliation even in drought‐adapted tree species such as the Mediterranean evergreen Quercus ilex L. The stomatal regulation of leaf water potential plays a central role in avoiding this phenomenon and is constrained by a suite of leaf traits including hydraulic conductance and vulnerability, hydraulic capacitance, minimum conductance to water vapour, osmotic potential and cell wall elasticity. We investigated whether the plasticity in these traits may improve leaf tolerance to drought in two long‐term rainfall exclusion experiments in Mediterranean forests. Osmotic adjustment was observed to lower the water potential at turgor loss in the rainfall‐exclusion treatments, thus suggesting a stomatal closure at more negative water potentials and a more anisohydric behaviour in drier conditions. Conversely, leaf hydraulic conductance and vulnerability did not exhibit any plasticity between treatments so the hydraulic safety margins were narrower in the rainfall‐exclusion treatments. The sequence of leaf responses to seasonal drought and dehydration was conserved among treatments and sites but trees were more likely to suffer losses of turgor and hydraulic functioning in the rainfall‐exclusion treatments. We conclude that leaf plasticity might help the trees to tolerate moderate drought but not to resist severe water stress. [ABSTRACT FROM AUTHOR]

Copyright of Academic Journal of Agriculture / Akademik Ziraat Dergisi is the property of University of Ordu, Faculty of Agriculture, Academic Journal of Agriculture and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Background and Aims Living root tissues significantly constrain plant water uptake under drought, but we lack functional traits to feasibly screen diverse plants for variation in the drought responses of these tissues. Water stress causes roots to lose volume and turgor, which are crucial to root structure, hydraulics and growth. Thus, we hypothesized that root pressure–volume (p–v) curve traits, which quantify the effects of water potential on bulk root turgor and volume, would capture differences in rootstock drought tolerance. Methods We used a greenhouse experiment to evaluate relationships between root p–v curve traits and gas exchange, whole-plant hydraulic conductance and biomass under drought for eight grapevine rootstocks that varied widely in drought performance in field trials (101-14, 110R, 420A, 5C, 140-Ru, 1103P, Ramsey and Riparia Gloire), grafted to the same scion variety (Vitis vinifera 'Chardonnay'). Key Results The traits varied significantly across rootstocks, and droughted vines significantly reduced root turgor loss point (π tlp), osmotic potential at full hydration (π o) and capacitance (C), indicating that roots became less susceptible to turgor loss and volumetric shrinkage. Rootstocks that retained a greater root volume (i.e. a lower C) also maintained more gas exchange under drought. The rootstocks that previous field trials have classified as drought tolerant exhibited significantly lower π tlp, π o and C values in well-watered conditions, but significantly higher π o and π tlp values under water stress, than the varieties classified as drought sensitive. Conclusions These findings suggest that acclimation in root p–v curve traits improves gas exchange in persistently dry conditions, potentially through impacts on root hydraulics or root to shoot chemical signalling. However, retaining turgor and volume in previously unstressed roots, as these roots deplete wet soil to moderately negative water potentials, could be more important to drought performance in the deep, highly heterogenous rooting zones which grapevines develop under field conditions. [ABSTRACT FROM AUTHOR]

Drought stress consists of a significant productivity constraint in tomatoes. Two contrasting crosses were performed to estimate physiological and morphological traits in response to drought stress during the vegetative stage, aiming to identify superior genotypes for drought tolerance. Two genotypes (GBT_2037 - sensitive drought-sensitive and GBT_2016 - intermediate drought-tolerant) were used as female parentals, and a commercial hybrid (drought tolerant) was used as a pollen source in both crosses: C1 (GBT_2037 x Commercial hybrid) and C2 (GBT_2016 x Commercial hybrid). The populations of parentals (P), the first generation of descendants (F1), backcrosses (BC), and the second generation of self-pollination (F2) were exposed to drought stress for 20 days when they were analyzed: physiological traits (relative water content of leaves, proline, and relative chlorophyll content) and morphological (plant height, stem diameter, number of leaves, fresh and dry matter of roots and shoot and classification by wilt scale). The means of chlorophyll, root/shoot ratio, and water content in leaves for the F2 generation of C2 were higher than C1, indicating that C2 resulted in plants with greater capacity to maintain turgor under conditions of water stress and presented minor damage to the photosynthetic structures, consequently showing greater tolerance to drought stress. [ABSTRACT FROM AUTHOR]

As future climates continue to change, precipitation deficits are expected to become more severe across tropical ecosystems. As a result, it is important that we identify plant physiological traits that act as adaptations to drought, and determine whether these traits act synergistically or independently of each other. In this study, we assessed the role of three leaf-level putative adaptations to drought: crassulacean acid metabolism (CAM), the turgor loss point (TLPΨ) and water storage hydrenchyma tissue. Using the genus Clusia as a model, we were able to explore the extent to which these leaf physiological traits co-vary, and also how they contribute to species' distributions across a precipitation gradient in Central and South America. We found that CAM is independent of the TLPΨ and hydrenchyma depth in Clusia. In addition, we provide evidence that constitutive CAM is an adaptation to year-long water deficits, whereas facultative CAM appears to be more important for surviving acute dry seasons. Finally, we find that the other leaf traits tested did not correlate with environmental precipitation, suggesting that the reduced transpirational rates associated with CAM obviate the need to adapt the TLPΨ and hydrenchyma depth in this genus. By identifying physiological traits more common in drier environments, it is possible to understand the ways in which tropical trees have adapted to deal with drought. By analysing a genus from Central and South America, we were able to test if it is more beneficial to prevent or tolerate water loss. Our results show that preventing water loss has a greater benefit to living in drier niches, which has implications for the ways in which future climates will affect tropical flora. [ABSTRACT FROM AUTHOR]

Summary: The effects of climate change on tropical forests will depend on how diverse tropical tree species respond to drought. Current distributions of evergreen and deciduous tree species across local and regional moisture gradients reflect their ability to tolerate drought stress, and might be explained by functional traits.We measured leaf water potential at turgor loss (i.e. 'wilting point'; πtlp), wood density (WD) and leaf mass per area (LMA) on 50 of the most abundant tree species in central Panama. We then tested their ability to explain distributions of evergreen and deciduous species within a 50 ha plot on Barro Colorado Island and across a 70 km rainfall gradient spanning the Isthmus of Panama.Among evergreen trees, species with lower πtlp were associated with drier habitats, with πtlp explaining 28% and 32% of habitat association on local and regional scales, respectively, greatly exceeding the predictive power of WD and LMA. In contrast, πtlp did not predict habitat associations among deciduous species.Across spatial scales, πtlp is a useful indicator of habitat preference for tropical tree species that retain their leaves during periods of water stress, and holds the potential to predict vegetation responses to climate change. [ABSTRACT FROM AUTHOR]

Summary: Under prolonged drought and reduced photosynthesis, plants consume stored nonstructural carbohydrates (NSCs). Stored NSC depletion may impair the regulation of plant water balance, but the underlying mechanisms are poorly understood, and whether such mechanisms are independent of plant water deficit is not known. If so, carbon costs of fungal symbionts could indirectly influence plant drought tolerance through stored NSC depletion.We connected well‐watered Pinus ponderosa seedling pairs via ectomycorrhizal (EM) networks where one seedling was shaded (D) and the other kept illuminated (LD) and compared responses to seedling pairs in full light (L). We measured plant NSCs, osmotic and water potential, and transfer of 13CO2 through EM to explore mechanisms linking stored NSCs to plant water balance regulation and identify potential tradeoffs between plant water retention and EM fungi under carbon‐limiting conditions.NSCs decreased from L to LD to D seedlings. Even without drought, NSC depletion impaired osmoregulation and turgor maintenance, both of which are critical for drought tolerance. Importantly, EM networks propagated NSC depletion and its negative effects on water retention from carbon stressed to nonstressed hosts.We demonstrate that NSC storage depletion influences turgor maintenance independently of plant water deficit and reveal carbon allocation tradeoffs between supporting fungal symbionts and retaining water. [ABSTRACT FROM AUTHOR]

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Summary: Maintaining water balance has been a critical constraint shaping the evolution of leaf form and function. However, flowers, which are heterotrophic and relatively short‐lived, may not be constrained by the same physiological and developmental factors.We measured physiological parameters derived from pressure–volume curves for leaves and flowers of 22 species to characterize the diversity of hydraulic traits in flowers and to determine whether flowers are governed by the same constraints as leaves.Compared with leaves, flowers had high saturated water content, which was a strong predictor of hydraulic capacitance in both leaves and flowers. Principal component analysis revealed that flowers occupied a different region of multivariate trait space than leaves and that hydraulic traits are more diverse in flowers than in leaves.Without needing to maintain high rates of transpiration, flowers rely on other hydraulic traits, such as high hydraulic capacitance, to maintain turgor pressure. As a result, instead of employing a metabolically expensive but durable carbon (C)‐based skeleton, flowers may rely predominantly on a metabolically cheaper, hydrostatic skeleton to keep their structures on display for pollinators, which has important implications for both the costs of reproduction and the biomechanical performance of flowers, particularly during drought. See also the Commentary on this article by Olson & Pittermann, 223: 8–10. [ABSTRACT FROM AUTHOR]

Drought tolerance shapes the distribution of plant species, and it is mainly determined by the osmotic potential at full turgor (π 0) and the water potential at turgor loss point (Ψ tlp). We provide a simplified framework for π 0 and Ψ tlp measurements based on osmometer determination of π 0 (π 0_osm). Specifically, we ran regression models to i) improve the predictive power of the estimation of π 0 from π 0_osm and morpho-anatomical traits; ii) obtain the most accurate model to predict Ψ tlp on the basis of the global relationship between π 0 and Ψ tlp. The inclusion of the leaf dry matter content (LDMC), an easy-to-measure trait, in the regression model improved the predictive power of the estimation of π 0 from π 0_osm. When π 0_osm was used as a simple predictor of Ψ tlp , discrepancies arose in comparison with global relationship between π 0 and Ψ tlp. Ψ tlp values calculated as a function of the π 0 derived from π 0_osm and LDMC (π 0_fit) were consistent with the global relationship between π 0 and Ψ tlp. The simplified framework provided here could encourage the inclusion of mechanistically sound drought tolerance traits in ecological studies. • Leaf turgor loss point (Ψ tlp) defines drought tolerance of plant species. • Ψ tlp could be estimated from the osmotic potential at full turgor (π 0). • π 0 could be easily measured with a dewpoint hygrometer. • Accounting for leaf dry matter content improves estimates of Ψ tlp from π 0. [ABSTRACT FROM AUTHOR]

Fertilization of woody plants plays a central role in agriculture and forestry, but little is known about how plant water relations are thereby affected. Here we investigated the impact of fertilization on tree hydraulics, and xylem and pit anatomy in the high-yield apple cultivars Golden and Red Delicious. In fertilized trees of Golden Delicious, specific hydraulic conductivity of branch xylem, hydraulic conductance of the root system, and maximum stomatal conductance increased considerably. In Red Delicious, differences between fertilized and control trees were less pronounced. In both cultivars, xylem embolism resistance of fertilized trees was significantly lower and stomatal closure occurred at lower water potentials. Furthermore, water potential at turgor loss point and osmotic potential at full saturation were higher and cell wall elasticity was lower in fertilized plants, suggesting reduced drought tolerance of leaves. Anatomical differences were observed regarding conduit diameters, cell wall reinforcement, pit membrane thickness, pit chamber depth, and stomatal pore length, with more pronounced differences in Golden Delicious. The findings reveal altered hydraulic behaviour in both apple cultivars upon fertilization. The increased vulnerability to hydraulic failure might pose a considerable risk for apple productivity under a changing climate, which should be considered for future cultivation and management practices. [ABSTRACT FROM AUTHOR]

The last years, Central European forests have suffered from drought as a direct consequence of climate change. All these forests have a long management history and it lies in the landowner's responsibility to replant damaged forests. Hence, landowners and the government are searching currently for species suitable to replant in areas affected by tree die-offs. It is a matter of fact that good knowledge of drought resistance of species is a critical measure for the current replanting efforts. We determined a widely recognized trait for leaf drought tolerance (leaf water potential at turgor loss point at full hydration, π tlp) in 41 woody species native or introduced in Central Europe. The osmometric rapid assessment method was used to measure the leaf osmotic potential at full hydration (π osm) of sun-exposed leaves and converted to π tlp. Mean π tlp of the native species was −2.33 ± 0.33 MPa. The less negative π tlp was found in the introduced species Aesculus hypocastania and was at −1.70 ± 0.11 MPa. The most negative π tlp, and thus the potentially highest drought tolerance, were found in the introduced species Pseudotsuga menzesii and was at −3.02 ± 0.14 MPa. High or less negative π tlp is associated with lower drought tolerance, whereas low or more negative π tlp stands for higher resistance to drought stress. For example, the two native species Illex aquifolium and Alnus glustinosa are species naturally associated with moist habitats and are characterized by the least negative π tlp of −1.75 ± 0.02 and −1.76 ± 0.03 MPa, respectively. [ABSTRACT FROM AUTHOR]

Clarifying the mechanisms of leaf and whole plant drought responses is critical to predict the impacts of ongoing climate change. The loss of rehydration capacity has been used for decades as a metric of leaf dehydration tolerance but has not been compared with other aspects of drought tolerance. We refined methods for quantifying the percent loss of rehydration capacity (PLRC), and for 18 Southern California woody species, we determined the relative water content and leaf water potential at PLRC of 10%, 25%, and 50%, and, additionally, the PLRC at important stages of dehydration including stomatal closure and turgor loss. On average, PLRC of 10% occurred below turgor loss point and at similar water status to 80% decline of stomatal conductance. As hypothesized, the sensitivity to loss of leaf rehydration capacity varied across species, leaf habits, and ecosystems and correlated with other drought tolerance traits, including the turgor loss point and structural traits including leaf mass per area. A new database of PLRC for 89 species from the global literature indicated greater leaf rehydration capacity in ecosystems with lower growing season moisture availability, indicating an adaptive role of leaf cell dehydration tolerance within the complex of drought tolerance traits. The capacity for leaves to rehydrate after dehydration has long been used as a metric of tissue desiccation tolerance. We refined a classical method for quantifying the percent loss of rehydration capacity (PLRC) for 18 Southern California woody species, compared this metric with other indices of drought tolerance, and placed the irreversible loss of rehydration capacity in the known sequence of leaf responses to drought. On average, across species, PLRC of 10% occurred below turgor loss point and at a similar water status as 80% stomatal closure. A compilation of PLRC data from the published literature showed strong variation across ecosystems, with ecosystems experiencing greater aridity in the growing season showing greater capacity for leaf rehydration. Our findings highlight leaf tissue desiccation tolerance as an adaptive trait and the importance of research establishing the mechanisms for leaf damage and resilience during and after drought. [ABSTRACT FROM AUTHOR]

Osmotic adjustment (OA), the accumulation of solutes in higher plant cells in response to water deficits, was first reported more than four decades ago. Since then, variation in OA among genotypes/cultivars in response to drought has been reported in many crop plants, but its role in maintaining growth and yield in water-limited environments has been questioned. The role of OA in the physiological and agronomic adaptation to water stress of crops, the methods of reliably measuring the degree of OA among genotypes or species, the range of OA in many studies, and its impact on grain yield in water-limited environments are reviewed. The genetics of OA has received limited study, and the breeding and selection for high OA has only resulted in the release of one commercial cultivar of wheat as far as is known. The reasons for the limited interest in breeding for the OA trait are discussed. [ABSTRACT FROM AUTHOR]

Abstract: Many plant species experience large differences in soil moisture availability within a season, potentially leading to a wide range of leaf water potentials (ΨLEAF). In order to decrease the risk of leaf dehydration, among species, there is a continuum ranging from strict control (isohydry) to little control (anisohydry) of minimum ΨLEAF. In central Texas USA, species are exposed to a range of soil moisture from wet springs to hot, dry summers. There are diverging water management strategies among the four dominant woody species in this system; two of these species are more isohydric (Prosopis glandulosa, Quercus fusiformis) while two others are more anisohydric (Diospyros texana, Juniperus asheii). To maintain leaf turgor and photosynthesis during periods of limited soil moisture, anisohydric species may adjust leaf hydraulic parameters more than isohydric species. To test this hypothesis, we quantified iso/anisohydry from 3 years of ΨLEAF predawn and midday measurements, and we measured the changes in turgor loss points (ΨTLP), osmotic potential at full hydration (Ψπ100), and resistance to leaf hydraulic dysfunction (leaf P50) throughout the spring and summer of 2016. Diospyros and Juniperus experienced more negative ΨLEAF and adjusted ΨTLP and Ψπ100 in response to both drying soils during the summer also in response to rainfall events during September. In contrast, the more isohydric species (Quercus and Prosopis) did not appear to adjust ΨTLP or Ψπ100 in response to soil moisture. The more anisohydric species also adjusted leaf P50 during periods of reduced soil moisture. Our results suggest that species that experience wider ranges of ΨLEAF have a greater ability to alter leaf hydraulic properties. This provides insight on how species with different strategies for water potential regulation may modify properties to mitigate drought effects in the future. A plain language summary is available for this article. [ABSTRACT FROM AUTHOR]

Main conclusion Drought tolerance was greater in the whole lichen than in its isolated photobiont. Cell turgor state has an influence on the functionality of photosynthetic process in lichens. Irreversible thermodynamics is widely used to describe the water relations of vascular plants. However, poikilohydrous organisms like lichens and aeroterrestrial microalgae have seldom been studied using this approach. Water relations of lichens are generally addressed without separate analysis of the mycobiont and photobiont, and only few studies have correlated changes in photosynthetic efficiency of dehydrating lichens to accurate measurements of their water potential components. We measured water potential isotherms and chlorophyll a fluorescence in the lichen Flavoparmelia caperata harvested in different seasons, as well as in its isolated photobiont, the green alga Trebouxia gelatinosa, either exposed to water stress cycles or fully hydrated. No significant seasonal trends were observed in lichen water relations parameters. Turgor loss point and osmotic potential of the whole thallus were significantly lower than those measured in the photobiont, while differences between the water stressed photobiont and controls were not significant. Dehydration-induced drop of Fv/Fm was correlated with turgor loss, revealing that the photosynthetic activity of lichens partly depends on their turgor level. We provided one of the first quantitative evidences of the influence that turgor status could exert on the functionality of photosynthetic processes in lichens. [ABSTRACT FROM AUTHOR]

In the Northeastern U.S., drought is expected to increase in frequency over the next century, and therefore, the responses of trees to drought are important to understand. There is recent debate about whether land-use change or moisture availability is the primary driver of changes in forest species composition in this region. Some argue that fire suppression from the early twentieth century to present has resulted in an increase in shade-tolerant and pyrophobic tree species that are drought intolerant, while others suggest precipitation variability as a major driver of species composition. From this debate, an emerging hypothesis is that mesophication and increases in the abundance of mesophytic genera (e.g., Acer, Betula, and Fagus) resulted in forests that are more vulnerable to drought. This review examines the published literature and factors that contribute to drought vulnerability of Northeastern U.S. forests. We assessed two key concepts related to drought vulnerability, including drought tolerance (ability to survive drought) and sensitivity (short-term responses to drought), with a focus on Northeastern U.S. species. We assessed drought-tolerance classifications for species, which revealed both consistencies and inconsistencies, as well as contradictions when compared to actual observations, such as higher mortality for drought-tolerant species. Related to drought sensitivity, recent work has focused on isohydric/anisohydric regulation of leaf water potential. However, based on the review of the literature, we conclude that drought sensitivity should be viewed in terms of multiple variables, including leaf abscission, stomatal sensitivity, turgor pressure, and dynamics of non-structural carbohydrates. Genera considered drought sensitive (e.g., Acer, Betula, and Liriodendron) may actually be less prone to drought-induced mortality and dieback than previously considered because stomatal regulation and leaf abscission in these species are effective at preventing water potential from reaching critical thresholds during extreme drought. Independent of drought-tolerance classification, trees are prone to dieback and mortality when additional stressors are involved such as insect defoliation, calcium and magnesium deficiency, nitrogen saturation, and freeze-thaw events. Overall, our literature review shows that multiple traits associated with drought sensitivity and tolerance are important as species may rely on different mechanisms to prevent hydraulic failure and depleted carbon reserves that may lead to mortality. [ABSTRACT FROM AUTHOR]

Plant-based techniques to measure crop water status offer advantages over soil-based methods. The objective of this study was to quantify the relationship between leaf thickness measurements, as a promising plant-based technique, with leaf relative water content (RWC) and assess the model across different species and leaf positions. The relationship between RWC and relative thickness (RT) was determined on corn ( Zea mays L.), sorghum ( Sorghum bicolor (L.) Moench), soybean ( Glycine max (L.) Merr.), and fava bean ( Vicia faba L.). RWC was calculated as measured leaf water content/leaf water content at full turgor, and RT as measured leaf thickness/leaf thickness at full turgor. Two leaves from the top, middle, and bottom of five plants of each species were collected at 60 days of age. Leaf samples brought to full turgor were left to dehydrate in a lab. Leaf thickness was measured using a magnetic field sensor and water content using weight loss. The RWC-RT relationship showed a distinct breakpoint, which we hypothesise coincides with the turgor loss point. Linear piecewise modelling was used to regress RWC versus RT, resulted in models explaining 86–97% of the variations. The precision was improved by including leaf position on the plant in the model. The piecewise model parameters were related to salt tolerance of the species, which is also an indicator of drought resistance. Generally, the species with greater drought and salinity tolerance had a larger RT at the breakpoint. [ABSTRACT FROM AUTHOR]

This study investigated the relationship between osmotic potential at full hydration (π100) and turgor loss point (ΨTLP) in wheat ( Triticum aestivum) to determine the potential of using π100 to predict ΨTLP under well-watered (WW) and drought (WS) conditions. Two methods for determining π100 were tested: pressure-volume (PV) analysis and freezing point osmometry. The study also measured π100 in a range of 38 field-grown wheat cultivars to determine whether there is genetic variation in π100 under field conditions. π100 correlated with ΨTLP using both methods under both water treatments, particularly WS. Genetic variation of π100 in the field, under rainfed conditions, was greater than controlled conditions and ranged from −0.94 to −1.95 MPa. Overall, the evidence supports development of π100 as a novel tool for plant breeders to screen large populations of wheat and identify genotypes with lower ΨTLP, an integrative trait that is related to drought tolerance. [ABSTRACT FROM AUTHOR]

The article discusses role of leaf turgor loss as a predictor of plant drought response strategies, referencing a research on leaf turgor loss point (TLP) published in this issue. It states that a meta-analysis of TLP and its relationship was conducted to a range of hydraulic traits linked to drought tolerance, as well as to leaf economic trait, and mentions that that species with higher TLP tend to have wider hydraulic safety margins. It notes role of TLP as an integrated and adaptive trait.

Amazonian droughts are predicted to become increasingly frequent and intense, and the vulnerability of Amazonian trees has become increasingly documented. However, little is known about the physiological mechanisms and the diversity of drought tolerance of tropical trees due to the lack of quantitative measurements., Leaf water potential at wilting or turgor loss point (πtlp) is a determinant of the tolerance of leaves to drought stress and contributes to plant-level physiological drought tolerance. Recently, it has been demonstrated that leaf osmotic water potential at full hydration (πo) is tightly correlated with πtlp. Estimating πtlp from osmometer measurements of πo is much faster than the standard pressure-volume curve approach of πtlp determination. We used this technique to estimate πtlp for 165 trees of 71 species, at three sites within forests in French Guiana. Our data set represents a significant increase in available data for this trait for tropical tree species., Tropical trees showed a wider range of drought tolerance than previously found in the literature, πtlp ranging from −1·4 to −3·2 MPa. This range likely corresponds in part to adaptation and acclimation to occasionally extreme droughts during the dry season., Leaf-level drought tolerance varied across species, in agreement with the available published observations of species variation in drought-induced mortality. On average, species with a more negative πtlp (i.e. with greater leaf-level drought tolerance) occurred less frequently across the region than drought-sensitive species., Across individuals, πtlp correlated positively but weakly with leaf toughness ( R2 = 0·22, P = 0·04) and leaf thickness ( R2 = 0·03, P = 0·03). No correlation was detected with other functional traits (leaf mass per area, leaf area, nitrogen or carbon concentrations, carbon isotope ratio, sapwood density or bark thickness)., The variability in πtlp among species indicates a potential for highly diverse species responses to drought within given forest communities. Given the weak correlations between πtlp and traditionally measured plant functional traits, vegetation models seeking to predict forest response to drought should integrate improved quantification of comparative drought tolerance among tree species. [ABSTRACT FROM AUTHOR]

Abiotic stresses collectively are responsible for crop losses worldwide. Among various abiotic stresses, drought and salinity are the most destructive. Different strategies have been adopted for the management of these stresses. Being complex traits, conventional breeding approaches have shown less success in improving salinity and drought stress tolerance. Roles of compatible solutes in salinity and drought stress tolerance have been studied extensively. At physiological level, osmotic adjustment is an adaptive mechanism involved in drought and/or salinity tolerance and permits the maintenance of turgor pressure under stress conditions. Increasing evidences from series of in vivo and in vitro studies involving physiological, biochemical, genetic, and molecular approaches strongly suggest that osmolytes such as ammonium compounds (polyamines, glycinebetaine, b-alanine betaine, dimethyl-sulfonio propionate and choline- O-sulfate), sugars and sugar alcohols (fructan, trehalose, mannitol, d-ononitol and sorbitol) and amino acids (proline and ectoine) perform important function in adjustment of plants against salinity and drought stresses. Thus, aim of this review is to expose how to osmoprotectants detoxify adverse effect of reactive oxygen species and alleviate drought and salinity stresses. An understanding of the relationship between these two sets of parameters is needed to develop measures for mitigating the damaging impacts of salinity and drought stresses. [ABSTRACT FROM AUTHOR]

Successful management of forest systems requires a deeper understanding of the role of ecophysiological traits in enabling adaptation to high temperature and water deficit under current and anticipated changes in climate. A key attribute of leaf water relations is the water potential at zero turgor (πtlp), because it defines the operating water potentials over which plants actively control growth and gas exchange. This study examines the drivers of variation in πtlp with respect to species climate of origin and habitat water availability. We compiled a water relations database for 174 woody species occupying clearly delineated gradients in temperature and precipitation across the Australian continent. A significant proportion of the variability in πtlp (∼35%) could be explained by climatic water deficit and its interaction with summertime maximum temperature, demonstrating the strong selective pressure of aridity and high temperature in shaping leaf water relations among Australian species. Habitat water availability (midday leaf water potential), was also a significant predictor of πtlp (R² = 0.43), highlighting the importance of species ecohydrologic niche under a set of climatic conditions. Shifts in πtlp in response to both climatic and site-based drivers of water availability emphasises its adaptive significance and its suitability as a predictor of plant performance under future climatic change. [ABSTRACT FROM AUTHOR]

In recent years, Central European forests and trees have been severely suffered from drought events in the growing season. To examine the tree growth response to drought stress, measurements of annual shoot lengths (ASL) of various tree species with distinct ages and habitats were taken in southeast Germany. The index of relative ASL increase (RAI), which is a standardized ASL increase, was calculated to indicate the growth rate of various tree species between the non-drought (2015–2017) and the drought period (2018–2020). The results showed the ASLs of most early-young trees (< 10 years) significantly showed a decreasing tendency in the drought period, whereas the middle-young (11–15 years) and late-young trees (> 16 years) presented a relatively stable trend. The ring-porous species with anisohydric behavior were likely to have higher RAIs associated with higher drought tolerance than diffuse-porous species with isohydric behavior. However, tree growth rate did not correlate with drought tolerance (resistance) of tree species indicated by leaf turgor loss point (Ψ tlp , MPa). Therefore, this study suggested parameters, such as growth rate, age phases, and microhabitats, should be considered to predict tree species' drought tolerance other than Ψ tlp. Finally, we emphasized tree shoot growth responses to drought were affected by multiple internal and external factors, and strongly depended on species- and site-specific characteristics, such as age phases, xylem structure, hydraulic strategy, microhabitat, grafting effect, and competition. ASL measurement can be recommended to be an easy, fast, and effective method to detect tree growth rate and response to environmental stress. [ABSTRACT FROM AUTHOR]

Many species face increasing drought under climate change. Plasticity has been predicted to strongly influence species' drought responses, but broad patterns in plasticity have not been examined for key drought tolerance traits, including turgor loss or 'wilting' point (πtlp). As soil dries, plants shift πtlp by accumulating solutes (i.e. 'osmotic adjustment'). We conducted the first global analysis of plasticity in Δπtlp and related traits for 283 wild and crop species in ecosystems worldwide. Δπtlp was widely prevalent but moderate (−0.44 MPa), accounting for 16% of post-drought πtlp. Thus, pre-drought πtlp was a considerably stronger predictor of post-drought πtlp across species of wild plants. For cultivars of certain crops Δπtlp accounted for major differences in post-drought πtlp. Climate was correlated with pre- and post-drought πtlp, but not Δπtlp. Thus, despite the wide prevalence of plasticity, πtlp measured in one season can reliably characterise most species' constitutive drought tolerances and distributions relative to water supply. [ABSTRACT FROM AUTHOR]

The drought tolerance of three economically important apple cultivars, Golden Delicious, Braeburn and Red Delicious, was analysed. The work offers insights into the hydraulics of these high-yield trees and indicates a possible hydraulic limitation of carbon gain. The hydraulic safety and efficiency of branch xylem and leaves were quantified, drought tolerance of living tissues was measured and stomatal regulation, turgor-loss point and osmotic potential at full turgor were analysed. Physiological measurements were correlated with anatomical parameters, such as conduit diameter, cell-wall reinforcement, stomatal density and stomatal pore length. Hydraulic safety differed considerably between the three cultivars with Golden Delicious being significantly less vulnerable to drought-induced embolism than Braeburn and Red Delicious. In Golden Delicious, leaves were less resistant than branch xylem, while in the other cultivars leaves were more resistant than branch xylem. Hydraulic efficiency and xylem anatomical measurements indicate differences in pit properties, which may also be responsible for variations in hydraulic safety. In all three cultivars, full stomatal closure occurred at water potentials where turgor had already been lost and severe loss of hydraulic conductivity as well as damage to living cells had been induced. The consequential negative safety margins pose a risk for hydraulic failure but facilitate carbon gain, which is further improved by the observed high stomatal conductance. Maximal stomatal conductance was clearly seen to be related to stomatal density and size. Based on our results, these three high-yield Malus domestica Borkh. cultivars span a wide range of drought tolerances, appear optimized for maximal carbon gain and, thus, all perform best under well-managed growing conditions. [ABSTRACT FROM AUTHOR]

* Premise of the study: Cultivated tomato, Solarium lycopersicum, suffers chilling induced wilting because water movement through its roots decreases with declining soil temperatures. Certain wild tomato species exhibit resistance to chilling-induced wilting, but the extent of this chilling tolerance in wild tomatoes is not known. * Methods: We measured shoot wilting during root chilling in wild Solarium accessions from habitats differing in elevation, temperature, and precipitation. We also measured shoot wilting during root chilling in introgression lines (ILs) with chromo some 9 segments collinear to the shoot turgor maintenance QTL stm9 region from chilling-tolerant S. habrochaites, chilling and drought-tolerant S. lycopersicoides, or drought-tolerant S. pennellii. * Key results: Wild tomato species, which experience chilling temperatures (<10°C) in their native habitat, maintain shoot turgor under root chilling. Among accessions of S. lycopersicum var. cerasiforme, a typically chilling sensitive species, shoot turgor maintenance during root chilling was correlated with the precipitation of the native habitat. By contrast, S. pennellii, a species that is typically drought adapted, did not maintain turgor under root chilling. Grafted plants with roots containing S. habrochaites and S. lycopersicoides introgressions improved shoot turgor maintenance under root chilling. * Conclusions: Resistance to chilling-induced water stress is an important adaptation to chilling temperatures in wild tomatoes. There is some overlap in adaptation to drought and chilling stress in some tomato species. Root-based resistance to chilling-induced water stress in wild tomatoes may involve orthologous gene(s). [ABSTRACT FROM AUTHOR]

ABSTRACT It is important to understand the ecophysiological characters of plants when exploring mechanisms underlying species substitution in the process of plant succession. In the present study, we selected 34 woody species from different stages of secondary succession in subtropical forests of southern China, and measured their hydraulic conductivity, gas exchange rates, leaf nutrients and drought-tolerance traits such as xylem resistance to cavitation, turgor loss point and carbon isotope ratio. Principal component analysis revealed that early-, mid- and late-successional species were significantly separated along axis 1, which was strongly associated with hydraulic-photosynthetic coordination. In contrast to species distributed in late-successional forest, early-successional species had the highest hydraulic conductivity, net photosynthetic rates, photosynthetic nitrogen and phosphorus use efficiencies, but had the lowest photosynthetic water-use efficiency. However, changes of the measured drought-tolerance traits of the 34 species along the succession did not demonstrate a clear trend - no significant correlations between these traits and plant successional stages were found. Moreover, the trade-off between hydraulic efficiency and safety was not identified. Taken together, our results suggested that hydraulic efficiency and photosynthetic function, rather than drought tolerance, play an important role in species distributions along plant succession in subtropical forests. [ABSTRACT FROM AUTHOR]

1. Across plant species, drought tolerance and distributions with respect to water availability are strongly correlated with two physiological traits, the leaf water potential at wilting, that is, turgor loss point (πtlp), and the cell solute potential at full hydration, that is, osmotic potential (πo). We present methods to determine these parameters 30 times more rapidly than the standard pressure-volume (p-v) curve approach, making feasible community-scale studies of plant drought tolerance. 2. We optimized existing methods for measurements of πo using vapour-pressure osmometry of freeze-thawed leaf discs from 30 species growing in two precipitation regimes, and developed the first regression relationships to accurately estimate pressure-volume curve values of both πo and πtlp from osmometer values. 3. The πo determined with the osmometer (πosm) was an excellent predictor of the πo determined from the p-v curve (πpv, r2 = 0·80). Although the correlation of πosm and πpv enabled prediction, the relationship departed from the 1 : 1 line. The discrepancy between the methods could be quantitatively accounted for by known sources of error in osmometer measurements, that is, dilution by the apoplastic water, and solute dissolution from destroyed cell walls. An even stronger prediction of πpv could be made using πosm, leaf density (ρ), and their interaction ( r2 = 0·85, all P < 2 × 10−10). 4. The πosm could also be used to predict πtlp ( r2 = 0·86). Indeed, πosm was a better predictor of πtlp than leaf mass per unit area (LMA; r2 = 0·54), leaf thickness (T; r2 = 0·12), ρ ( r2 = 0·63), and leaf dry matter content (LDMC; r2 = 0·60), which have been previously proposed as drought tolerance indicators. Models combining πosm with LMA, T, ρ, or LDMC or other p-v curve parameters (i.e. elasticity and apoplastic fraction) did not significantly improve prediction of πtlp. 5. This osmometer method enables accurate measurements of drought tolerance traits across a wide range of leaf types and for plants with diverse habitat preferences, with a fraction of effort of previous methods. We expect it to have wide application for predicting species responses to climate variability and for assessing ecological and evolutionary variation in drought tolerance in natural populations and agricultural cultivars. [ABSTRACT FROM AUTHOR]

Water deficit is a major problem in semi arid regions of Pakistan. It affects plant growth, yield and eventually leads to a considerable crop failure. Although maize (Zea mays L.) is susceptible to water deficit there is a marked genotypic variation in rooting density, morphological and physiological characteristics in maize. A green house experiment was conducted to study the response of spring maize plant growth to soil moisture content under controlled conditions. The seeds of eight maize hybrids (FH 421, FH 810, Pioneer 32-F-10, Pioneer 32-W-86, Monsanto 919, Monsanto 6525, NK 8441 & SS 5050) were sown in pots having the capacity of eight kg soil. A factorial completely randomized design (CRD) with three replications was used. The two field capacities (75% & 100%) were maintained after the reduction of 30% soil moisture. Monsanto 919 performed better in both levels with maximum plant height, leaf area per plant, water potential, osmotic potential, turgor potential and minimum relative saturation deficit, while maize hybrid FH 810 remained sensitive at deficit irrigation (75% field capacity). [ABSTRACT FROM AUTHOR]

• Hard leaves commonly occur in water- and nutrient-limited habitats. • Some anatomical features conferring mechanical resistance can also assure drought tolerance. • Thick cell walls and high major vein density allow leaves to endure water shortage. Leaves of terrestrial plants vary tremendously in size, shape, and stiffness. Hard leaves with high mass per unit area (LMA) occur more frequently in water- and nutrient-limited habitats, where stress-tolerance is key to survival. Coordination between leaf mechanical properties and drought tolerance can arise because some (but not all) of the anatomical modifications leading to high LMA are mechanistically correlated to physiological traits conferring tolerance to dehydration. Thick cell walls are frequently coupled with low turgor loss point values, and also prevent cell shrinkage and collapse after turgor loss has occurred. This also protects the leaf against shrinking-induced loss of water transport capacity in the extra-vascular pathway. In turn, vascular water transport in the leaf veins is at risk of embolism-induced disruption under drought, but higher length of major veins per unit area can provide alternative pathways for water delivery to the mesophyll, while contributing to increased leaf stiffness. Water shortage in dry and warm habitats implies the risk of reduced photosynthetic rates, apparently favouring species that produce hard and drought-tolerant leaves, to warrant long leaf life span and to maintain gas exchange and positive carbon gain when conditions become harsh. [ABSTRACT FROM AUTHOR]

In all studies of the effects of water deficits on plant functioning there is a need for an accurate and comprehensive definition of treatments and their effects on plant water status. The various measures of water status used in plant and soil science are reviewed and their appropriateness for different purposes such as for studies of mechanistic effects of water deficits on plants, for breeding of drought-tolerant plants, or for management of irrigation systems are reviewed. An important conclusion is that the frequent emphasis on water potential rather than on cell turgor can be shown to be misleading, as can be measurements in the leaf. The disadvantages of the current trend towards the omission of necessary water-status measurements, especially common in more molecular studies, are outlined, and recommendations made for minimal sets of measurements for specific types of experiments. [ABSTRACT FROM PUBLISHER]