MCA: Crossing Disciplines to Link Nutrients in Tree Canopy, Soils, and Stream Water to Mineral Weathering in a Tropical Forest

尽管热带森林流域只覆盖了地球无冰陆地的13%，但它们含有大约一半储存在地球表面植物中的碳，这使得它们在储存碳方面变得不成比例地重要。大气中二氧化碳的增加已被证明可以增加植物的生物量，从而从大气中去除二氧化碳，并将其隔离在生物圈中。然而，植物的生长可能会受到营养限制的限制，阻止植物通过光合作用将较高的二氧化碳水平转化为生物量。增加生态系统养分有效性的一种方法是通过风化或地球表面岩石和矿物的分解来调动基岩中的养分。这项研究活动将直接解决这些问题，同时有助于职业生涯中期的研究人员的职业发展。大气中二氧化碳的增加可以增加光合作用，但其他因素，包括养分限制、干旱和土壤中碳动态的变化，可能会影响热带森林吸收二氧化碳的能力，从而将热带森林从碳汇变成碳源。这项研究将解决一个潜在的限制因素(养分限制)，并评估日益加剧的风化是否能够以足够快的速度提供基岩衍生的养分，从而影响森林生产力。研究人员将在波多黎各西南部两个霓虹灯观测站的四个采样点测试这一假说：生长在营养贫乏的蛇纹岩上的植物是否依赖快速矿物风化来抵消基岩的低营养含量？Rio Cupeyes的气候梯度采样点将测试温度和降雨量的增加对蛇纹岩基岩低营养生态系统中通过化学风化获得养分的影响。里约热内卢吉拉特的第四个地点将作为一个对照，并允许预测基岩化学和养分释放。研究人员将通过三项任务解决这一假设：(I)测量所有相关水库的养分、主要元素和微量元素化学，包括基岩、土壤、土壤水、树叶、树叶凋落物、大气沉降和里约热内卢Cupeyes的三个气候梯度地点以及里约热内卢的一个对照地点的溪水；(Ii)利用土坑、土壤水样和溪流输出总量来量化里约库佩耶斯和里奥吉拉特岛的化学风化速率；以及(3)利用遥感图像对里奥库佩耶斯三个地点和里奥吉拉特州一个地点的地上总生物量进行建模，并在气候梯度上进行比较，以测试气温和降水增加对生态系统生产力的影响。通过使用从溪流化学和森林土壤的时间整合的长期风化剖面计算的整个生态系统通量计算风化释放的养分，研究人员将比较发生在两个时间和空间尺度上的养分释放和化学风化。然后将这些风化模型与遥感数据中的景观生产力估计值进行比较，以检查风化速率是否与树木的生物量生产相关。该项目由地球科学部的地球生物学和低温地球化学计划和既定的激励竞争性研究计划(EPSCoR)共同资助。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。

Although forested tropical watersheds cover just 13 percent of Earth’s ice-free land mass, they contain approximately half of the carbon that is stored in plants on Earth’s surface, making them disproportionately important in storing carbon. Increased carbon dioxide in the atmosphere has been shown to increase plant biomass, thereby removing carbon dioxide from the atmosphere and sequestering it in the biosphere. However, plant growth can be limited by nutrient limitation, preventing plants from converting higher carbon dioxide levels into biomass through photosynthesis. One way to increase nutrient availability to ecosystems is to mobilize nutrients from bedrock through weathering, or the breaking down of rocks and minerals at Earth’s surface. This research activity will directly address these issues, while contributing to the career development of a mid-career researcher.Increased atmospheric CO2 can increase photosynthesis, but other factors, including nutrient limitation, drought, and changes to carbon dynamics in soils may affect tropical forests’ abilities to take up CO2, thereby turning tropical forests from a carbon sink to a carbon source. This study will address one potential limiting factor (nutrient limitation) and assess whether increased weathering can provide bedrock-derived nutrients at a fast enough rate to affect forest productivity. The researchers will test the hypothesis “Do plants growing on nutrient-poor serpentinite rely on rapid mineral weathering to offset the low nutrient content of the bedrock?,” at four sampling sites at two NEON observatories in southwestern Puerto Rico. Sampling locations across a climate gradient at Rio Cupeyes will test the effect of increasing temperature and rainfall on nutrient acquisition via chemical weathering in a low nutrient ecosystem on serpentinite bedrock. The fourth site at Rio Guilarte will serve as a control as well as allow predictions about bedrock chemistry and nutrient release. The researchers will address this hypothesis through three tasks: (i) measure the nutrient, major element, and trace element chemistry of all relevant reservoirs including bedrock, soil, soil water, leaves, leaf litter, atmospheric deposition, and stream water at three sites along a climate gradient at Rio Cupeyes as well as a control site at Rio Guilarte; (ii) quantify chemical weathering rates at Rio Cupeyes and Rio Guilarte using soil pits, soil water samples, and total export via streams; and (iii) model total aboveground biomass at all three Rio Cupeyes sites and one Rio Guilarte site using remote sensing imagery and compare these across the climate gradient to test the effect of increasing temperature and precipitation on ecosystem productivity. By calculating nutrient release via weathering using whole ecosystem fluxes calculated from stream chemistry and time-integrated, long term weathering profiles from forest soils, the researchers will compare nutrient release and chemical weathering occurring over two temporal and spatial scales. These weathering models will then be compared to landscape productivity estimates from remote sensing data to examine whether weathering rate is correlated to biomass production by trees. This project is jointly funded by the Geobiology and Low-Temperature Geochemistry Program in the Division of Earth Sciences and the Established Program to Stimulate Competitive Research (EPSCoR).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.