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Copyright of Journal of Biogeography is the property of Wiley-Blackwell 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.)

Copyright of Journal of Ecology is the property of Wiley-Blackwell 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.)

Copyright of Functional Ecology is the property of Wiley-Blackwell 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.)

Summary: Tropical ecosystems have the highest levels of biodiversity, cycle more water and absorb more carbon than any other terrestrial ecosystem on Earth. Consequently, these ecosystems are extremely important components of Earth's climatic system and biogeochemical cycles. Plant hydraulics is an essential discipline to understand and predict the dynamics of tropical vegetation in scenarios of changing water availability. Using published plant hydraulic data we show that the trade‐off between drought avoidance (expressed as deep‐rooting, deciduousness and capacitance) and hydraulic safety (P50 – the water potential when plants lose 50% of their maximum hydraulic conductivity) is a major axis of physiological variation across tropical ecosystems. We also propose a novel and independent axis of hydraulic trait variation linking vulnerability to hydraulic failure (expressed as the hydraulic safety margin (HSM)) and growth, where inherent fast‐growing plants have lower HSM compared to slow‐growing plants. We surmise that soil nutrients are fundamental drivers of tropical community assembly determining the distribution and abundance of the slow‐safe/fast‐risky strategies. We conclude showing that including either the growth‐HSM or the resistance‐avoidance trade‐off in models can make simulated tropical rainforest communities substantially more vulnerable to drought than similar communities without the trade‐off. These results suggest that vegetation models need to represent hydraulic trade‐off axes to accurately project the functioning and distribution of tropical ecosystems. [ABSTRACT FROM AUTHOR]

Ecologists seek a general scheme to classify the diversity of plant responses to environmental factors into a few strategies (e.g. competitor—C, stress tolerant—S, ruderal—R), while plant physiologists seek a mechanistic scheme to explain such different responses (e.g. tolerance, escape, avoidance). So far, few attempts have been made to combine both perspectives into plant eco‐physiological strategies. Moreover, the relative contribution of different strategies to maintain both community structure and ecosystem functioning during drought has rarely been assessed. Thus, limiting our capacity to predict how extreme events caused by climate change will affect plant communities.Here, we present an integrated framework to identify plant eco‐physiological strategies and to estimate their contribution to community originality (diversity of trait combinations), dominance (species relative frequency) and ecosystem functioning (productivity and evapotranspiration).We applied this framework in a tropical montane grassland in Brazil (Campos de Altitude) and found three eco‐physiological strategies co‐occurring in this community (S‐tolerance/avoidance, CS‐escape/tolerance and CR‐escape/avoidance). While CS‐species contributed more to dominance and functionality, CR‐ and S‐species contributed more to originality. Therefore, all three strategies were important to support the grassland form and function.Synthesis. Plants exhibit different strategies, as well as different contributions to community and ecosystem attributes. We developed an integrated approach to both identify strategies and estimate their relative contribution. Thereby, as droughts intensify, we can better predict which plants are more likely to be lost and how their loss will impact the communities and ecosystem where they occur. This knowledge is necessary for specifying conservation priorities and for developing more efficient conservation practices. [ABSTRACT FROM AUTHOR]

Summary: Land surface models (LSMs) typically use empirical functions to represent vegetation responses to soil drought. These functions largely neglect recent advances in plant ecophysiology that link xylem hydraulic functioning with stomatal responses to climate.We developed an analytical stomatal optimization model based on xylem hydraulics (SOX) to predict plant responses to drought. Coupling SOX to the Joint UK Land Environment Simulator (JULES) LSM, we conducted a global evaluation of SOX against leaf‐ and ecosystem‐level observations.SOX simulates leaf stomatal conductance responses to climate for woody plants more accurately and parsimoniously than the existing JULES stomatal conductance model. An ecosystem‐level evaluation at 70 eddy flux sites shows that SOX decreases the sensitivity of gross primary productivity (GPP) to soil moisture, which improves the model agreement with observations and increases the predicted annual GPP by 30% in relation to JULES. SOX decreases JULES root‐mean‐square error in GPP by up to 45% in evergreen tropical forests, and can simulate realistic patterns of canopy water potential and soil water dynamics at the studied sites.SOX provides a parsimonious way to incorporate recent advances in plant hydraulics and optimality theory into LSMs, and an alternative to empirical stress factors. See also the Commentary on this article by Anderegg & Venturas, 226: 1535–1538. [ABSTRACT FROM AUTHOR]

Many tropical montane cloud forest (TMCF) trees are capable of foliar water uptake (FWU) during leaf-wetting events. In this study, we tested the hypothesis that maintenance of leaf turgor during periods of fog exposure and soil drought is related to species' FWU capacity., We conducted several experiments using apoplastic tracers, deuterium labeling and leaf immersion in water to evaluate differences in FWU among three common TMCF tree species. We also measured the effect of regular fog exposure on the leaf water potential of plants subjected to soil drought and used these data to model species' response to long-term drought., All species were able to absorb water through their leaf cuticles and/or trichomes, although the capacity to do so differed between species. During the drought experiment, the species with higher FWU capacity maintained leaf turgor for a longer period when exposed to fog, whereas the species with lower FWU exerted tighter stomatal regulation to maintain leaf turgor. Model results suggest that without fog, species with high FWU are more likely to lose turgor during seasonal droughts., We show that leaf-wetting events are essential for trees with high FWU, which tend to be more anisohydric, maintaining leaf turgor during seasonal droughts. [ABSTRACT FROM AUTHOR]

In Brazil, the campos rupestres occur over the Brazilian shield, and are characterized by acidic nutrient-impoverished soils, which are particularly low in phosphorus (P). Despite recognition of the campos rupestres as a global biodiversity hotspot, little is known about the diversity of P-acquisition strategies and other aspects of plant mineral nutrition in this region., To explore nutrient-acquisition strategies and assess aspects of plant P nutrition, we measured leaf P and nitrogen (N) concentrations, characterized root morphology and determined the percentage arbuscular mycorrhizal ( AM) colonization of 50 dominant species in six communities, representing a gradient of soil P availability. Leaf manganese (Mn) concentration was measured as a proxy for carboxylate-releasing strategies., Communities on the most P-impoverished soils had the highest proportion of nonmycorrhizal ( NM) species, the lowest percentage of mycorrhizal colonization, and the greatest diversity of root specializations. The large spectrum of leaf P concentration and variation in root morphologies show high functional diversity for nutritional strategies. Higher leaf Mn concentrations were observed in NM compared with AM species, indicating that carboxylate-releasing P-mobilizing strategies are likely to be present in NM species., The soils of the campos rupestres are similar to the most P-impoverished soils in the world. The prevalence of NM strategies indicates a strong global functional convergence in plant mineral nutrition strategies among severely P-impoverished ecosystems. [ABSTRACT FROM AUTHOR]

Foliar water uptake ( FWU) is a common water acquisition mechanism for plants inhabiting temperate fog-affected ecosystems, but the prevalence and consequences of this process for the water and carbon balance of tropical cloud forest species are unknown., We performed a series of experiments under field and glasshouse conditions using a combination of methods (sap flow, fluorescent apoplastic tracers and stable isotopes) to trace fog water movement from foliage to belowground components of Drimys brasiliensis. In addition, we measured leaf water potential, leaf gas exchange, leaf water repellency and growth of plants under contrasting soil water availabilities and fog exposure in glasshouse experiments to evaluate FWU effects on the water and carbon balance of D. brasiliensis saplings., Fog water diffused directly through leaf cuticles and contributed up to 42% of total foliar water content. FWU caused reversals in sap flow in stems and roots of up to 26% of daily maximum transpiration. Fog water transported through the xylem reached belowground pools and enhanced leaf water potential, photosynthesis, stomatal conductance and growth relative to plants sheltered from fog., Foliar uptake of fog water is an important water acquisition mechanism that can mitigate the deleterious effects of soil water deficits for D. brasiliensis. [ABSTRACT FROM AUTHOR]