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

了解大片热带雨林将如何应对气候变化，包括日益频繁的干旱，这一点很重要，因为这些森林在地球的碳循环中扮演着重要角色。该奖项提供资金，用于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。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对干旱更具弹性。这些结果将被用来模拟和预测森林物种构成的差异如何导致整个森林对干旱的反应不同。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在巴西进行研究。将通过生物圈2的外联计划和科学节提高公众对这些问题的认识，科学节促进每年向100多名中学生介绍亚马逊。植物干旱反应的科学在很大程度上假定环境调节光合作用的碳源(碳源调节)，然后根据固定的异速生长规则将碳源分配给生长和其他功能。然而，有一种新的观点认为，植物内部的C-库过程(生长、储存和呼吸)直接受到环境和植物内部反馈的调节(C-库调节假说)，因此分配和库过程的变化是干旱反应的关键机制。现实地将这种机制推广到生态系统规模，需要考虑到不同植物经济光谱中不同物种的策略。为了切实验证这一假说，我将面临以下挑战：通过整合一系列水力特征的树木C源(光合作用)和C库(生长、储存、呼吸)过程的测量，以确定调控机制；通过关注资源和植物水力特征在植物经济光谱上的分布，将干旱响应机制提升到生态系统水平；以及观察生态系统规模的光合碳源(总生态系统生产力，GEP)和蒸腾失水。这项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C动态的理解，以及对气候变化下森林未来的评估。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。

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.