Collaborative Research: Terrestrial Denitrification and Environmental Change

氮是一种重要的植物养分，它的可用性常常限制树木的生长。微生物反硝化过程从生态系统中去除可用氮，并产生一系列氮气，包括一氧化二氮，一种强效温室气体。地球系统模型往往无法捕捉到这些氮气损失的幅度或全球分布。反硝化发生在低氧条件下，由于分析挑战和巨大的时空变化，测量变得复杂。该项目将采用一套测量方法来检验几种环境因素调节反硝化作用的假设，并将在一个重要的地球系统模型中改进反硝化作用的表示。该研究对氮作为空气和水污染物的调控政策具有重要意义，对地球系统模型的改进为预测未来环境变化的国际科学和政策计划提供了支持。该项目将通过在新罕布什尔州哈伯德布鲁克实验森林进行的实地研究和以社区土地模型（CLM-CN）为代表的研究来促进对反硝化环境调节的理解。在Hubbard Brook，该项目将测试几种环境因素的作用，包括土壤氧含量、土壤深度、降雨量变化、土壤变暖和土壤酸化。该项目将部署测量方法，包括基于土壤核的氮气通量、连续土壤氧传感器、基于室内的气体通量和硝酸盐稳定同位素。这些测量结果将提供反硝化及其环境驱动因素的综合评估，并将使该项目能够改善群落土地模型中植物-微生物竞争和碳-氮-氧生物地球化学的代表性。该项目还将培训两名研究生和一名博士后，并将为不同群体的研究生提供动手生物地球化学新兵训练营，学习用于测量温室气体排放和相关生态系统过程的先进技术。

Nitrogen is a vital plant nutrient, and its availability often limits tree growth. The microbial process of denitrification removes available nitrogen from ecosystems and produces a range of nitrogen gases, including nitrous oxide, a potent greenhouse gas. Earth system models often fail to capture the magnitude or global distribution of these nitrogen gas losses. Denitrification occurs under low-oxygen conditions, and measurements are complicated by both analytical challenges and tremendous spatial and temporal variation. This project will apply a suite of measurement approaches to test hypotheses about the way that several environmental factors regulate denitrification, and it will improve the representation of denitrification in an important earth system model. This research has important implications for policies regulating nitrogen as an air and water pollutant, and improvements to the earth system model support international science and policy programs for predicting future environmental change.This project will advance understanding of the environmental regulation of denitrification in both field studies at the Hubbard Brook Experimental Forest in New Hampshire and as represented by the Community Land Model (CLM-CN). At Hubbard Brook, the project will test the role of several environmental factors hypothesized to regulate denitrification, including soil oxygen levels, soil depth, rainfall variability, soil warming, and soil acidification. The project will deploy measurement approaches that include soil core-based fluxes of nitrogen gases, continuous soil oxygen sensors, chamber-based gas fluxes, and nitrate stable isotopes. Together these measurements will provide a comprehensive assessment of denitrification and its environmental drivers, and will enable this project to improve representation of plant-microbe competition and carbon-nitrogen-oxygen biogeochemistry in the Community Land Model. The project will also train two graduate students and one postdoctoral associate, and it will offer hands-on biogeochemistry boot camps for diverse groups of graduate students on the advanced techniques used for measuring greenhouse gas emissions and related ecosystem processes.