Collaborative Research: The coordinated structural and physiological responses of trees to water stress: an organismal approach

干旱是一个全球性且日益频繁的问题，它威胁着森林的活力及其为社会提供的诸多益处（包括固碳、木材供应和水循环调节）。树木在干旱期间是茁壮成长还是枯萎，取决于它们对这些压力条件的反应。尽管有许多关于干旱期间叶片水平对光合作用和水分利用的变化的研究，但尚不清楚树木如何在整个植物尺度上进行综合和协调的变化。例如，改变叶子角度的树木可以减少树冠不同层次的辐射负荷，减少热应力和水分损失。本研究采用干旱试验方法研究了水分胁迫下树冠结构与生理的协调调节。研究人员将叶片和冠层气体交换的传统测量与测量冠层结构和生理的新型遥感技术结合在一起。该项目将通过与非营利组织（Math4Science）合作，提供跨学科的教学、培训和学习经验，该组织推广STEM，制作3D森林视频，指导本科生，并让代表性不足群体的K-12学生接触STEM研究。森林将在多大程度上继续充当碳汇和减缓气候变化，取决于树木是否能够进行生理和结构调整，以应对不断变化的环境压力。迄今为止，大多数关于树木对干旱反应的研究都集中在树木如何改变叶片水平的生理、物候和碳的动员和分配。然而，树木也会对干旱做出结构调整（例如，通过改变叶片角度），以减少辐射负荷和叶片温度。该研究将目前植物水分利用策略的研究从叶片或生态系统尺度的生理反应扩展到冠层结构（叶片角度）的新维度。研究人员的目标是回答“树木通过冠层结构和叶片生理的协调调整在多大程度上响应水分胁迫，以及通过什么机制？”将叶片和冠层气体交换的测量与测量冠层结构和叶片生理的新型遥感技术（包括地面激光扫描（TLS）和无人驾驶汽车（UAV））相结合。通过利用经典和新颖的技术，该项目将为植物在空间（叶片到冠层）和时间尺度（短期到长期）上对水分胁迫的协调反应提供新的见解。在整个树冠尺度的干旱生理研究中纳入机械响应将为干旱科学提供新的机制见解，并将有助于建立生态系统尺度模型的综合机制方法。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Drought is a global and increasingly frequent problem that threatens the vitality of forests and the many benefits they provide to society (including carbon sequestration, timber provisioning, and water cycle regulation). Whether trees thrive or falter during drought depends on how they respond to these stressful conditions. Despite many studies of leaf-level changes to photosynthesis and water use during drought, it is still unclear how trees make integrated and coordinated changes at the scale of the entire plant. For example, trees that change the angles of their leaves can reduce the radiation load at different levels of the canopy, reducing heat stress and water loss. This study investigates the coordinated adjustments of tree canopy structure and physiology under water stress using drought experiments in both growth chambers and in a forest that has a rainfall removal experiment. The investigators bring together traditional measurements of leaf and canopy gas exchange with novel remote sensing techniques that measure canopy structure and physiology. This project will provide interdisciplinary teaching, training, and learning experiences by collaborating with a non-profit organization (Math4Science) that promotes STEM, creating videos of 3D forests, mentoring undergraduate students, and exposing K-12 students from under-represented groups to STEM research.The degree to which forests will continue to serve as carbon sinks and mitigate climate change hinges on whether trees can make physiological and structural adjustments to cope with changing environmental stressors. Most research to date on tree responses to drought has focused on how trees alter leaf-level physiology, phenology, and carbon mobilization and allocation. However, trees also make structural adjustments in response to drought (e.g., by changing leaf angles) to reduce radiation load and leaf temperature. The work extends current research on plant water use strategies, which is mostly focused on physiological responses at the leaf or ecosystem scales, to a new dimension - canopy structure (leaf angles). The investigators aim to answer the question "To what extent do trees respond to water stress through coordinated adjustments of canopy structure and leaf physiology, and by what mechanisms?" combining measurements of leaf and canopy gas exchange with novel remote sensing techniques that measure canopy structure and leaf physiology, including the Terrestrial Laser Scanning (TLS) and the Unmanned Autonomous Vehicle (UAV). By taking advantage of both classical and novel techniques, this project will provide new insights into the coordination of plant response to water stress over spatial (leaf to canopy) and temporal scales (short to long term). Including mechanical responses in physiological studies of drought at the scales of entire tree crowns will provide novel mechanistic insights into drought-science and will facilitate building comprehensive mechanistic approaches into ecosystem-scale models.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.