RII Track 4: Arctic Nitrous Oxide (N2O): Training and Technical Advances to Quantify Emission of a Powerful Greenhouse Gas

一氧化二氮是一种强效温室气体，其气候变暖潜能值约为二氧化碳的300倍。氧化亚氮是由微生物在土壤和沉积物中循环氮产生并释放到大气中的，通常是对过量氮的反应。高纬度生态系统通常对大气的氧化亚氮贡献很少，因为有利于氧化亚氮产生的氮的形式有限。然而，越来越多的记录显示，受到低温扰动或永久冻土融化影响的北极和亚北极土壤中有异常大的氧化亚氮通量。目前尚不清楚这种一氧化二氮是如何产生的，以及受到干扰的土壤可能会在多长时间内产生排放物。这个项目将支持几种分析方法的培训，以确定土壤中氧化亚氮产生的数量和途径。研究将集中在阿拉斯加受野火和永久冻土融化影响的生态系统上。研究人员还将适应并应用稳定同位素的新方法来确定产生氧化亚氮的微生物途径。确定一氧化二氮是如何产生的，将减少预测生态系统如何对不断变化的火灾和永久冻土制度作出反应的不确定性，并澄清生态系统如何反过来影响气候系统。过去十年的几项研究记录了永久冻土正在融化的北极土壤中大量排放的一氧化二氮（N2O）。然而，这些研究尚未揭示产生N2O的生物过程，其中可能包括反硝化、硝化和硝化-反硝化。由于高纬度土壤中N2O产生的途径仍然未知，目前很难预测高纬度生态系统在更温暖、更富营养和更容易发生火灾的条件下的潜在排放。一个位于阿拉斯加的研究团队将与加里生态系统研究所的氮分析设备合作，应用和优化新的分析方法。这些研究将包括根据操纵土壤条件实时产生N2O，以及同位素分析（描述15N的位置偏好），这可以确定微生物产生N2O的途径。这些方法将应用于降水事件、季节、连续时间尺度和空间梯度，包括阿拉斯加内陆空间不连续永久冻土区域内氮输入、永久冻土和燃烧历史的变化。该研究的目标包括确定高纬度土壤中产生一氧化二氮的微生物途径，并测试氮循环与北方森林的火灾、永久冻土和水分状况之间的假设关系。建立这些关系是确定高纬度生态系统中氮循环与气候变暖之间潜在的正反馈回路的重要一步。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。

Nitrous oxide is a potent greenhouse gas, with about ~300 times the climate warming potential of carbon dioxide. Nitrous oxide is produced and released to the atmosphere by microbes that cycle nitrogen in soils and sediment, often in response to excess nitrogen. High-latitude ecosystems typically contribute little nitrous oxide to the atmosphere because of limited availability of the forms of nitrogen conducive to nitrous oxide production. However, exceptionally large fluxes of nitrous oxide are increasingly documented from arctic and sub-arctic soils that are subject to cryoturbation or thawing permafrost. It remains unclear how this nitrous oxide is produced and how long disturbed soils might generate emissions. This project will support training in several analytical approaches for determining the quantity and pathways of nitrous oxide production in soils. Research will focus on Alaskan ecosystems that are subject to wildfire and permafrost thaw. Researchers will also adapt and apply novel methods with stable isotopes to determine the microbial pathways producing nitrous oxide. Determining how nitrous oxide is produced will decrease uncertainty in predicting how ecosystems respond to changing regimes of fire and permafrost and clarify how ecosystems might in turn influence the climate system. Several studies over the past decade have documented significant emissions of nitrous oxide (N2O) from arctic soils where permafrost is thawing. However, these studies have not revealed the biological processes generating N2O, which might include denitrification, nitrification, and nitrifier-denitrification. Because the pathways of N2O production in high-latitude soils remain unknown, it is presently difficult to forecast potential emissions under warmer, more nutrient-rich, and fire-prone conditions predicted for high-latitude ecosystems. An Alaska-based research team will work with the nitrogen analytical facility at the Cary Institute of Ecosystem Studies to apply and optimize novel analytical approaches. These studies will include real-time production of N2O in response to manipulated soil conditions, and analysis of isotopomers (describing site preference of 15N), which can identify the microbial pathway producing N2O. These approaches will be applied across precipitation events, seasonal, and successional time scales and spatial gradients encompassing variation in nitrogen inputs, permafrost, and burn history within the region of spatially discontinuous permafrost in Interior Alaska. Goals of the research include identifying the microbial pathways that produce N2O in high-latitude soils and testing hypothesized relationships between nitrogen cycling and the fire, permafrost, and moisture regimes of the boreal forest. Establishing these relationships is an essential step toward identifying potential positive feedback loops between nitrogen cycling and climate warming in high-latitude ecosystems.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.