Collaborative Research: Are Amazon forest trees source or sink limited? Mapping hydraulic traits to carbon allocation strategies to decipher forest function during drought

了解大面积的热带森林将如何应对气候变化，包括干旱频率的增加，是很重要的，因为这些森林在地球的碳循环中发挥着重要作用。该奖项为研究亚马逊森林将如何应对最近厄尔尼诺现象所经历的干旱提供了资金。研究人员将研究单个物种如何捕获和利用碳和水，并利用这些数据来了解物种的生物多样性如何使整个森林更能抵御干旱。这些结果将被整合到模拟和预测森林物种组成的差异如何导致整个森林对干旱的不同反应。该奖项将评估生物群落的组成如何影响其整体功能，以及未来变化对整个热带森林的影响。该项目将促进国际合作和培训美国本科生到巴西做研究。提高公众对这些问题的认识将通过生物圈2的推广项目和科学节来实现，科学节每年向100多名初高中学生提供关于亚马逊的有针对性的演讲。植物干旱响应科学在很大程度上假设环境调节光合碳源（“c源调节”），然后根据固定的异速生长规则将其分配给生长和其他功能。然而，有一种新兴的观点认为，植物内部的碳汇过程（生长、储存和呼吸）直接受到环境和植物内部反馈的调节（“碳汇调节”假说），因此分配和碳汇过程的变化是干旱响应的关键机制。现实地将这种机制推广到生态系统规模需要考虑在植物经济光谱中变化的物种特定策略。为了实际验证这一假设，以下挑战将通过整合测量树木c源（光合作用）和c汇（生长、储存、呼吸）过程，通过一系列水力特性来确定调节机制；将干旱响应机制提升到生态系统水平，重点关注资源和植物水力性状的分布，映射到植物经济谱；观察生态系统尺度的光合C源（生态系统总生产力，GEP）和蒸腾造成的水分损失。对树木碳源和碳汇过程控制的评估——包括Kok效应、非结构性碳储存和植物水分关系——将改变我们对亚马逊森林碳动态的理解和对气候变化下森林未来的评估。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。

Understanding how large expanses of tropical forests will respond to climate variation, including increasing frequency of droughts, is important since these forests play a big role in the planet's carbon cycle. This award provides funds to study how the Amazon forest will respond to droughts such as experienced in the recent El Nino. Researchers will examine how individual species capture and use carbon and water, and use that data to understand how biodiversity of species makes the whole forest more resilient to droughts. The results will be integrated to model and predict how differences in forest species composition result in differences in whole-forest responses to drought. This award will evaluate how composition of biological communities influences their overall function and the effects of future changes on entire tropical forests. The project will advance international collaboration and the training of U.S. undergraduates to do research in Brazil. Increased public awareness of these issues will occur through outreach programs at the Biosphere 2, and a Science Festival which facilitates targeted presentations about the Amazon to 100+ middle-high school students/year. The science of plant drought response has largely assumed that environment regulates photosynthetic source of carbon ('C-source regulation'), which is then allocated to growth and other functions according to fixed allometric rules. There is an emerging view, however, that within-plant C-sink processes (growth, storage, and respiration) are directly regulated by the environment and by within-plant feedbacks (the 'C-sink regulation' hypothesis), such that changes in allocation and sink processes are a key mechanism of drought response. Realistically propagating such mechanisms to the ecosystem scale requires accounting for species-specific strategies that vary across the plant economic spectrum. To realistically test this hypothesis, the following challenges will be me through integrating measurements of tree C-source (photosynthesis) and C-sink (growth, storage, respiration) processes across a range of hydraulic traits to identify regulating mechanisms; Upscaling the mechanisms of drought response to the ecosystem level by focusing on distributions of both resources and plant hydraulic traits mapped to the plant economic spectrum; and Observing the ecosystem-scale photosynthetic C source (Gross Ecosystem Productivity, GEP) and water loss by transpiration. This evaluation of the controls on tree C-source and C-sink processes - including the Kok effect, Non-Structural C storage, and plant water relations - will transform our understanding of Amazon forest C dynamics and assessment of the forest's future under climate change.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.