LTREB: How does inter-annual variation in rainfall interact with soil fertility and chronic disruption of soil moisture dynamics to alter soil C cycling in tropical forests?

许多热带森林正在经历干旱和降雨事件变化的增加。热带森林是地球上最多样化的生态系统之一，拥有全球植物和土壤中最大的碳储量。因此，它们是一个“碳库”，以固体形式储存碳，并减少大气中潜在的碳作为温室气体二氧化碳（CO2）。因此，这些生态系统对全球社会的生物多样性、养分循环和气候调节至关重要。该项目研究干燥对热带森林碳储存和循环的影响，采用了一项长期实验，减少了巴拿马四种不同热带森林的降雨投入。森林的背景降雨量和土壤肥力不同，这可能会影响它们对干旱的反应。该项目成立于2015年，因此正在积累长期数据集。在最初的7年数据中，碳通量和碳循环每年都有很大的变化，这可能与不同年份之间降雨量的变化有关。这个名为“巴拿马热带雨林实验干燥变化”（PARCHED）的新项目现在将继续进行额外的5 - 10年测量。这些结果将有助于提高对热带森林碳储量在几十年内如何响应气候变率变化的理解。本科生将有机会参与研究，并将有英语和西班牙语制作的宣传材料。过去7年PARCHED实验的结果与预测有一些异常。一些模型预测与实验结果相匹配，而一些不匹配表明热带森林的重要过程没有在模型中表现出来。特别是，模型没有考虑到土壤中水通量减少的重要性，以及与之相关的土壤养分输送减少的重要性，而这在降雨和土壤水文年际变化的背景下可能是重要的。该项目致力于：a)确定观测到的慢性干燥对热带碳循环年的影响是否在10至20年的背景降雨变化中持续存在；B)允许检测热带森林长期土壤碳储量的变化。该项目测量树木的茎和根生长、土壤碳水平以及通过二氧化碳通量从土壤中损失的碳的变化。正在进行的工作旨在改进干旱下热带雨林重要过程的模型表征。在开展这些科学活动时，该项目培训和支持一名全职现场技术人员，包括本科生研究人员，并将作为史密森尼科学推广工作的一部分。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。

Many tropical forests are experiencing drying and increased variation in rainfall events. Tropical forests are among the most diverse ecosystems on Earth and hold some of the largest stocks of carbon in plants and soils globally. Thus, they are a “carbon bank,” storing carbon in solid form and reducing potential carbon in the atmosphere as the greenhouse gas carbon dioxide (CO2). Therefore, these ecosystems are important to global societies for biodiversity, nutrient cycling, and climate moderation. This project studies the effects of drying on carbon storage and cycling in tropical forests, using a long-term experiment that reduces rainfall inputs to four distinct tropical forests in Panama. The forests have different background rainfall and soil fertility, which could influence how they respond to drying. The project was established in 2015, and thus is accumulating a long-term dataset. In the initial seven years of data there was large variation in carbon fluxes and cycling from year to year, possibly related to variation in rainfall between different years. This new project, called Panama Rainforest Changes with Experimental Drying (PARCHED), will now continue for an additional 5 – 10 years of measurements. These results will help improve understanding of how tropical forest carbon storage changes over decades in response to climate variability. Undergraduate students will have opportunities to be involved in research, and there will be outreach materials produced in both English and Spanish. Results from the past seven years of the PARCHED experiment have some anomalies relative to what would be predicted. Some model predictions matched experimental results, while some mismatches suggested that important processes in tropical forests were not represented in the model. In particular, the importance of reduced water fluxes into soils, and related reductions in delivery of nutrients into soils, were lacking from the model, which could be important in the context of inter-annual variation in rainfall and soil hydrology. This project works to: a) determine whether observed chronic drying effects on tropical carbon cycling years persist over one to two decades of background rainfall variation; b) allow for detection of changes in long-term soil carbon storage in tropical forests. The project measures tree stem and root growth, soil carbon levels, and changes in carbon losses from soils via CO2 fluxes. Ongoing work aims to improve the model characterization of important processes in rainforests under drying. In conducting these scientific activities, the project trains and support a full-time field technician, involves undergraduate researchers, and will be used as part of the Smithsonian’s science outreach efforts.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.