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有力的温室气体，其气候变暖潜力约为二氧化碳的300倍。一氧化二氮是由土壤和沉积物中循环氮的微生物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很少向大气中排放一氧化二氮，因为有利于一氧化二氮产生的氮的形式有限。然而，异常大的一氧化二氮通量越来越多地记录从北极和亚北极土壤，受到低温扰动或融化的永久冻土。目前还不清楚这种一氧化二氮是如何产生的，以及受干扰的土壤会在多长时间内产生排放。该项目将支持在确定土壤中一氧化二氮产生的数量和途径的若干分析方法方面的培训。研究将集中在受野火和永久冻土融化影响的阿拉斯加生态系统。研究人员还将调整和应用具有稳定同位素的新方法来确定产生一氧化二氮的微生物途径。确定一氧化二氮是如何产生的将减少预测生态系统如何应对火灾和永久冻土变化的不确定性，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已经证明，在永久冻土融化的北极土壤中，一氧化二氮（N2 O）的排放量很大。然而，这些研究并没有揭示产生N2 O的生物过程，这可能包括反硝化，硝化和硝化-反硝化。由于高纬度土壤中N2 O产生的途径仍然未知，目前很难预测在高纬度生态系统预测的更温暖、更富营养和易发生火灾的条件下的潜在排放量。一个位于阿拉斯加的研究小组将与卡里生态系统研究所的氮分析设施合作，应用和优化新的分析方法。这些研究将包括实时生产的N2 O响应操纵土壤条件，和同位素分析（描述15 N的网站偏好），这可以确定微生物途径产生N2 O。这些方法将适用于整个降水事件，季节性和演替的时间尺度和空间梯度，包括氮输入的变化，永久冻土，并在阿拉斯加内陆的空间不连续的永久冻土区内的燃烧历史。该研究的目标包括确定在高纬度土壤中产生N2 O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和气候变暖之间潜在正反馈回路的重要一步。该奖项反映了NSF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.