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Analysis of functional traits is a cornerstone of ecology, yet individual traits seldom explain useful amounts of variation in species distribution or climatic tolerance, and their functional significance is rarely validated experimentally. Multivariate suites of interacting traits could build an understanding of ecological processes and improve our ability to make sound predictions of species success in our rapidly changing world. We use foliar water uptake capacity as a case study because it is increasingly considered to be a key functional trait in plant ecology due to its importance for stress‐tolerance physiology. However, the traits behind the trait, that is, the features of leaves that determine variation in foliar water uptake rates, have not been assembled into a widely applicable framework for uptake prediction. Focusing on trees, we investigated relationships among 25 structural traits, leaf osmotic potential (a source of free energy to draw water into leaves), and foliar water uptake in 10 diverse angiosperm and conifer species. We identified consistent, multitrait "uptake syndromes" for both angiosperm and conifer trees, with differences in key traits revealing suspected differences in the water entry route between these two clades and an evolutionarily significant divergence in the function of homologous structures. A literature review of uptake‐associated functional traits, which largely documents similar univariate relationships, provides additional support for our proposed "uptake syndrome." Importantly, more than half of shared traits had opposite‐direction influences on the capacity of leaves to absorb water in angiosperms and conifers. Taxonomically targeted multivariate trait syndromes provide a useful tool for trait selection in ecological research, while highlighting the importance of micro‐traits and the physiological verification of their function for advancing trait‐based ecology. [ABSTRACT FROM AUTHOR]

Absorption of water across the surfaces of leaves is an ecologically important aspect of tree physiology. Variation in foliar water uptake capacity depends on environmental conditions when traits associated with the uptake pathway respond to climatic signals. Using a series of experiments, we verify that water enters Sequoia sempervirens (D. Don) Endl. leaves by crossing the cuticle, and show that surface-trait acclimation alters the kinetic parameters of foliar water uptake. Under our experimental conditions, the cuticle was the primary pathway for water entry into the leaf. Exposure to climatic variation may induce surface acclimations, such as increased waxiness, that reduce water-film formation over stomata at the expense of dry-season foliar uptake rates. We found that water uptake is negatively associated with the interaction of leaf-surface wax coverage and stomatal density, and provide an accessible protocol to measure these key traits in Sequoia. Linking absorptive pathways and trait acclimation to physiological performance can provide a foundation for range-wide or genomic investigations of forest interactions with water and a mechanism-centered means to monitor canopy hydraulic parameters over time. [ABSTRACT FROM AUTHOR]

Tracheid buckling may protect leaves in the dynamic environments of forest canopies, where rapid intensifications of evaporative demand, such as those brought on by changes in light availability, can result in sudden increases in transpiration rate. While treetop leaves function in reliably direct light, leaves below the upper crown must tolerate rapid, thermally driven increases in evaporative demand. Using synchrotron‐based X‐ray microtomography, we visualized impacts of experimentally induced water stress and subsequent fogging on living cells in redwood leaves, adding ecological and functional context through crown‐wide explorations of variation in leaf physiology and microclimate. Under drought, leaf transfusion tracheids buckle, releasing water that supplies sufficient temporal reserves for leaves to reduce stomatal conductance safely while stopping the further rise of tension. Tracheid buckling fraction decreases with height and is closely coordinated with transfusion tissue capacity and stomatal conductance to provide temporal reserves optimized for local variation in microclimate. Foliar water uptake fully restores collapsed and air‐filled transfusion tracheids in leaves on excised shoots, suggesting that trees may use aerial water sources for recovery. In the intensely variable deep‐crown environment, foliar water uptake can allow for repetitive cycles of tracheid buckling and unbuckling, protecting the tree from damaging levels of hydraulic tension and supporting leaf survival. If sudden changes in microclimate increase transpirational demand, tracheid buckling in the water‐filled transfusion tissue of Sequoia sempervirens leaves can release a quantity of water sufficient to briefly sustain increased transpiration, thereby providing time for stomatal adjustment. The temporal reserves supplied by tracheid buckling can be replenished through foliar water uptake, which allows collapsed tracheids to refill to their former volumes. [ABSTRACT FROM AUTHOR]

Premise: Trees in wet forests often have features that prevent water films from covering stomata and inhibiting gas exchange, while many trees in drier environments use foliar water uptake to reduce water stress. In forests with both wet and dry seasons, evergreen trees would benefit from producing leaves capable of balancing rainy‐season photosynthesis with summertime water absorption. Methods: Using samples collected from across the vertical gradient in tall redwood (Sequoia sempervirens) crowns, we estimated tree‐level foliar water uptake and employed physics‐based causative modeling to identify key functional traits that determine uptake potential by setting hydraulic resistance. Results: We showed that Sequoia has two functionally distinct shoot morphotypes. While most shoots specialize in photosynthesis, the axial shoot type is capable of much greater foliar water uptake, and its within‐crown distribution varies with latitude. A suite of leaf surface traits cause hydraulic resistance, leading to variation in uptake capacity among samples. Conclusions: Shoot dimorphism gives tall Sequoia trees the capacity to absorb up to 48 kg H2O h−1 during the first hour of leaf wetting, ameliorating water stress while presumably maintaining high photosynthetic capacity year round. Geographic variation in shoot dimorphism suggests that plasticity in shoot‐type distribution and leaf surface traits helps Sequoia maintain a dominate presence in both wet and dry forests. [ABSTRACT FROM AUTHOR]

SUMMARY: Drought is a major limitation for survival and growth in plants. With more frequent and severe drought episodes occurring due to climate change, it is imperative to understand the genomic and physiological basis of drought tolerance to be able to predict how species will respond in the future. In this study, univariate and multitrait multivariate genome‐wide association study methods were used to identify candidate genes in two iconic and ecosystem‐dominating species of the western USA, coast redwood and giant sequoia, using 10 drought‐related physiological and anatomical traits and genome‐wide sequence‐capture single nucleotide polymorphisms. Population‐level phenotypic variation was found in carbon isotope discrimination, osmotic pressure at full turgor, xylem hydraulic diameter, and total area of transporting fibers in both species. Our study identified new 78 new marker × trait associations in coast redwood and six in giant sequoia, with genes involved in a range of metabolic, stress, and signaling pathways, among other functions. This study contributes to a better understanding of the genomic basis of drought tolerance in long‐generation conifers and helps guide current and future conservation efforts in the species. Significance Statement: Climate change brings more frequent and severe drought events that challenge the survival of natural populations of plants. While most of our knowledge about drought tolerance comes from annual and domesticated plants, the genomic basis of drought tolerance in long‐generation trees is poorly understood. Here, we aim to fill this gap by identifying candidate genes in two conifer species, coast redwood and giant sequoia. [ABSTRACT FROM AUTHOR]

Premise of the study: Leaves are the sites of greatest water stress in trees and a key means of acclimation to the environment. We considered phenotypic plasticity of Pseudotsuga menziesii leaves in their ecological context, exploring responsiveness to natural gradients in water stress (indicated by sample height) and light availability (measured from hemispherical photos) to understand how leaf structure is controlled by abiotic factors in tall tree crowns. Methods: After measuring anatomy, morphology, and carbon isotope composition (δ13C) of leaves throughout crowns of P. menziesii >90 m tall, we compared structural plasticity of leaves among the three tallest conifer species using equivalent data from past work on Sequoia sempervirens and Picea sitchensis. Key results: Leaf mass per projected area (LMA) and δ13C increased and mesoporosity (airspace/area) decreased along the water‐stress gradient, while light did not play a detectable role in leaf development. Overall, leaves of P. menziesii were far less phenotypically responsive to within‐crown abiotic gradients than either P. sitchensis, whose leaves responded strongly to light availability, or S. sempervirens, whose leaves responded equally strongly to water stress. Conclusions: P. menziesii maintain remarkably consistent leaf structure despite pronounced vertical gradients in abiotic factors. Contrasting patterns of leaf structural plasticity underlie divergent ecological strategies of the three tallest conifer species, which coexist in Californian rainforests. [ABSTRACT FROM AUTHOR]

In recent years, tree-ring databases have emerged as a remarkable resource for ecological research, allowing us to address ecological questions at unprecedented temporal and spatial scales. However, concerns regarding big tree-ring data limitations and risks have also surfaced, leading to questions about their potential to be representative of long-term forest responses. Here, we highlight three paths of action to improve on tree-ring databases in ecology: 1) Implementing consistent bias analyses in large dendroecological databases and promoting community-driven data to address data limitations, 2) Encouraging the integration of tree-ring data with other ecological datasets, and 3) Promoting theory-driven, mechanistic dendroecological research. These issues are increasingly important for tackling pressing cross-disciplinary research questions. Finally, although we focus here on tree ring databases, these points apply broadly across many aggregative databases in ecology., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)