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

干旱是一个日益频繁的全球性问题，威胁着森林的生命力及其为社会提供的许多好处(包括碳封存、木材供应和水循环调节)。树木在干旱期间是茁壮成长还是摇摇欲坠，取决于它们对这些压力条件的反应。尽管对干旱期间叶片水平对光合作用和水分利用的影响进行了许多研究，但仍不清楚树木如何在整个植物的尺度上进行综合和协调的变化。例如，改变树叶角度的树木可以减少树冠不同层次的辐射负荷，从而减少热压力和水分损失。本研究通过室内干旱试验和森林降水去除试验，研究了水分胁迫下树木冠层结构与生理的协调调节。研究人员将树叶和树冠气体交换的传统测量与测量树冠结构和生理的新型遥感技术结合在一起。该项目将通过与一个促进STEM的非营利性组织(Math4Science)合作，提供跨学科的教学、培训和学习经验，制作3D森林的视频，指导本科生，并让未被充分代表的群体的K-12学生参与STEM研究。森林将在多大程度上继续作为碳汇和缓解气候变化，取决于树木是否能够做出生理和结构调整，以应对不断变化的环境压力。到目前为止，大多数关于树木对干旱的反应的研究都集中在树木如何改变叶片水平的生理、物候以及碳的动员和分配。然而，树木也因应干旱(例如，通过改变叶片角度)进行结构调整，以减少辐射负荷和叶片温度。这项工作将当前关于植物水分利用策略的研究从主要集中在叶片或生态系统尺度上的生理响应扩展到一个新的维度-冠层结构(叶片角度)。研究人员的目标是回答这样一个问题：“树木通过树冠结构和叶片生理的协调调整，在多大程度上对水分胁迫做出反应，以及通过什么机制？”将树叶和树冠气体交换的测量与测量树冠结构和树叶生理的新型遥感技术相结合，包括地面激光扫描(TLS)和无人自主飞行器(UAV)。通过利用经典和新技术，该项目将为植物对水分胁迫的空间(叶到树冠)和时间尺度(短期到长期)的协调提供新的见解。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械学见解，并将促进将全面的机械学方法建立到生态系统规模的模型中。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.