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

尽管森林覆盖的热带流域只占地球无冰陆地面积的13%，但它们含有地球表面植物中储存的碳的大约一半，这使得它们在储存碳方面具有不成比例的重要作用。大气中二氧化碳的增加已被证明会增加植物生物量，从而从大气中去除二氧化碳并将其隔离在生物圈中。然而，植物的生长可能受到营养限制，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。增加生态系统养分可用性的一种方法是通过风化作用或地球表面岩石和矿物质的分解，从基岩中调动养分。这项研究活动将直接解决这些问题，同时有助于职业中期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转变为碳源。这项研究将解决一个潜在的限制因素（营养限制），并评估风化作用的增加是否能够以足够快的速度提供基岩来源的营养物质，从而影响森林生产力。研究人员将测试这样一个假设：“在营养贫乏的蛇纹岩上生长的植物是否依赖于快速的矿物风化来抵消基岩的低营养含量？”在波多黎各西南部的两个NEON观测站的四个采样点进行了测试。在里约热内卢Cupeyes的气候梯度上取样，将测试在蛇纹岩基岩的低营养生态系统中，温度和降雨的增加对通过化学风化获取营养物质的影响。位于里约热内卢Guilarte的第四个地点将作为对照，并允许预测基岩化学和营养物质释放。研究人员将通过三个任务来解决这一假设：(i)测量所有相关水库的营养物质、主元素和微量元素化学，包括基岩、土壤、土壤水、树叶、凋落叶、大气沉积和溪水，在里约热内卢Cupeyes沿着气候梯度的三个地点以及里约热内卢Guilarte的对照地点；（ii）利用土坑、土壤水样和通过溪流出口的总量，量化里约热内卢Cupeyes和里约热内卢Guilarte的化学风化速率；（iii）利用遥感图像模拟所有三个里约热内卢Cupeyes站点和一个里约热内卢Guilarte站点的地上总生物量，并在气候梯度上进行比较，以测试温度和降水增加对生态系统生产力的影响。通过利用河流化学和森林土壤长期风化剖面计算出的整个生态系统通量来计算风化过程中的养分释放，研究人员将比较两个时空尺度上发生的养分释放和化学风化。然后将这些风化模型与来自遥感数据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促进竞争性研究的既定计划（EPSCoR）共同资助。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。

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.