Dissertation Research: Carbon Sequestration in a Subalpine Forest and Its Control by Winter and Summer Precipitation Dynamics

本研究的重点是了解两个重要的生物地球化学循环：碳循环和水循环之间的耦合。在被假设为美国西部主要碳汇的亚高山森林生态系统中，树木生长和土壤微生物活性受到水分有效性的高度控制。该项目旨在了解不同降水类型（冬雪和夏雨）如何影响该生态系统的碳吸收。通过分析最近固定的糖的碳同位素比率，将计算全年树木水分利用效率（WUE）的测量值。然后将开发一个模型，通过测量水分利用效率和蒸腾来计算碳同化。为了研究降水类型对森林碳吸收的影响，将利用氧和氢同位素追踪树木利用的水源，并将优势水源与森林碳增益相关。

The focus of this research is to understand the coupling between two important biogeochemical cycles: the carbon and water cycle. In the subalpine forest ecosystem, which has been hypothesized as a major carbon sink in the Western U.S., tree growth and soil microorganism activity are highly controlled by the availability of moisture. This project aims to understand how different precipitation types (winter snow versus summer rains) affect carbon uptake in this ecosystem. By analyzing the carbon isotope ratio of recently fixed sugars, measurements of tree water use efficiency (WUE) will be calculated throughout the year. A model will then be developed to calculate carbon assimilation from measurements of WUE and transpiration. Oxygen and hydrogen isotopes will be used to trace water sources used by trees, and the dominant water source will be related to forest carbon gain in order to investigate the influences of precipitation type on forest carbon uptake.