Rainwater uptake in conifer twigs: five experiments tell a story of absorption, storage, and transport.

While evidence supports the idea that a portion of the many raindrops that fall onto a forest canopy may be directly absorbed by the twigs they land on, we do not know how much is absorbed, how it enters the twig, or what internal path it might take on its way to the xylem. Using a diverse series of five experiments encompassing isotopic labelling, fluorescent tracers, rehydration kinetics, synchrotron-based X-ray tomographic microscopy, and thermal imaging, we follow the fate of rainwater from initial contact with the twig to its distribution to adjacent tissues. We provide conclusive, multi-pronged evidence of surface water-absorption into the xylem of 1-year-old conifer twigs with incomplete bark development.

The memory of past water abundance shapes trees 7 years later.

Premise: Tree structure and function are constrained by and acclimate to climatic conditions. Drought limits plant growth and carbon acquisition and can result in "legacy" effects that last beyond the period of water stress. Leaf and twig-level legacy effects of past water abundance, such as that experienced by trees that established under wetter conditions are unknown.

Moving ecological tree-ring big data forwards: Limitations, data integration, and multidisciplinarity.

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.

Seed classification with random forest models.

Premise: To improve forest conservation monitoring, we developed a protocol to automatically count and identify the seeds of plant species with minimal resource requirements, making the process more efficient and less dependent on human operators.

Methods And Results: Seeds from six North American conifer tree species were separated from leaf litter and imaged on a flatbed scanner. In the most successful species-classification approach, an ImageJ macro automatically extracted measurements for random forest classification in the software R.

Towards multivariate functional trait syndromes: Predicting foliar water uptake in trees.

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.

Acclimation of interacting leaf surface traits affects foliar water uptake.

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.

Tracheid buckling buys time, foliar water uptake pays it back: Coordination of leaf structure and function in tall redwood trees.

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.

Shoot dimorphism enables Sequoia sempervirens to separate requirements for foliar water uptake and photosynthesis.

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.

Ray fractions and carbohydrate dynamics of tree species along a 2750 m elevation gradient indicate climate response, not spatial storage limitation.

Parenchyma cells in the xylem store nonstructural carbohydrates (NSC), providing reserves of energy that fuel woody perennials through periods of stress and/or limitations to photosynthesis. If the capacity for storage is subject to selection, then the fraction of wood occupied by living parenchyma should increase towards stressful environments. Ray parenchyma fraction (RPF) and seasonal NSC dynamics were quantified for 12 conifers and three oaks along a transect spanning warm dry foothills (500 m above sea level) to cold wet treeline (3250 m asl) in California's central Sierra Nevada.

Within-crown plasticity in leaf traits among the tallest conifers.

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 (δ C) of leaves throughout crowns of P.

Leaf acclimation to light availability supports rapid growth in tall Picea sitchensis trees.

Leaf-level anatomical variation is readily apparent within tall tree crowns, yet the relative importance of water and light availability in controlling this variation remains unclear. Sitka spruce (Picea sitchensis, (Bong.) Carr.

Phenotypic plasticity of leaves enhances water-stress tolerance and promotes hydraulic conductivity in a tall conifer.

Premise Of The Study: Leaves respond to environmental signals and acclimate to local conditions until their ecological limits are reached. Understanding the relationships between anatomical variation in leaves and the availability of water and light improves our ability to predict ecosystem-level impacts of foliar response to climate change, as it expands our knowledge of tree physiology.

Methods: We examined foliar anatomy and morphology of the largest plant species, Sequoiadendron giganteum, from leafy shoot samples collected throughout crowns of trees up to 95 m tall and assessed the functionality of within-crown variation with a novel drought/recovery experiment.