Do biological processes result in the 17-O mass independent anomaly in atmospheric nitrous oxide? Resolution and establishment of 17-O as a tracer of microbial production

一氧化二氮(N2O)是过去150年来人类导致全球变暖趋势的三种最重要的生物温室气体之一。因此，N2O也是温室气体核算实践的一个组成部分，并包括在欧洲和美国的碳市场(即芝加哥气候交易所)。尽管政府间气候变化专门委员会最近的努力平衡了全球N2O预算，但仍存在巨大的不确定性。地球上几乎所有的物质在氧的17O和18O同位素之间具有一致的关系，这被称为质量相关性。然而，对流层N2O相对于质量依赖的氧在17O中富集了0.9？长期以来，N2O中的这种17O异常一直被认为反映了平流层中光化学反应产生的17O的并入以及平流层和对流层之间的N2O交换。最近有人提出，N2O中的17O异常是生物产生的，是微生物生产过程中水中的氧气进入N2O的结果。如果正确，这将是第一次观察到生物产生的170度异常。在这项建议中，PIS将测试三种机制，通过这些机制可以将17O异常引入生物产生的N2O中：(1)与水交换，(2)O2和水中的氧的差异结合，以及(3)携带17O异常的大气硝酸盐的反硝化作用。此外，他们将通过无机紫外光氧化来测试生产过程中是否存在17O异常。PIs将采用多种方法来评估生物N2O产生17O异常的可能性，包括从纯化的酶、纯微生物培养和农业土壤培养中产生N2O。生物产生的N2O中17O异常的存在对了解大气N2O的来源和IPCC等国际组织对这种重要温室气体的全球预算具有深远影响。将开发的微生物产生N2O的仪器、方法和知识将成为密歇根州立大学一个短期课程的组成部分，该课程涉及来自全国各地的研究生、教授和专业人员(稳定同位素生物地球化学)。该项目还将涉及机械、电气和计算机工程专业的本科生团队，他们将开发和部署涡流协方差痕量气体捕集系统，该系统将能够在植物树冠中收集足够数量的N2O，以限制土壤中N2O进入大气的等量通量。

Nitrous oxide (N2O) is one of the three most important biogenic greenhouse gases contributing to the human induced global warming trend over the past 150 years. Consequently, N2O is also an integral component of greenhouse gas accounting practices and included in both European and U.S. carbon markets (i.e. the Chicago Climate Exchange). While recent efforts by the IPCC have balanced the global N2O budget, great uncertainty remains. Nearly all materials on Earth have a consistent relationship between the 17O and 18O isotopes of oxygen that is termed mass dependence. Tropospheric N2O, however, is enriched in 17O relative to oxygen in mass dependence by 0.9 ?. This 17O anomaly in N2O has long been considered to reflect incorporation of 17O from photochemical reactions in the stratosphere and exchange of N2O between the stratosphere and troposphere. Recently it has been proposed that the 17O anomaly in N2O is biologically produced and the result of incorporation of oxygen from water into N2O during its microbial production. If correct, this would be the first observation of a biologically produced 17O anomaly. In this proposal the PIs will test three mechanisms by which the 17O anomaly may be introduced into biologically produced N2O: (1) exchange with water, (2) differential incorporation of oxygen from O2 and water, and (3) denitrification of atmospheric nitrate that carries a 17O anomaly. Further, they will test for the presence of a 17O anomaly during production by inorganic UV photo-oxidation. The PIs will pursue a variety of approaches to evaluate the potential for biological N2O to generate a 17O anomaly that includes production of N2O from purified enzymes, pure microbial cultures and incubation of agricultural soils.The presence of a 17O anomaly in biologically produced N2O has profound implications for understanding the origin of atmospheric N2O and the global budget of this important greenhouse gas by international organizations such as the IPCC. The instrumentation, methodologies, and knowledge of microbial N2O production that will be developed will become an integral component of a short course at MSU that involves graduate students, professors and professionals from across the country (Stable Isotope Biogeochemistry). The project will also involve a team undergraduate mechanical, electrical and computer engineering students who will develop and deploy an Eddy-covariance Trace Gas Trapping System that will enable collection of sufficient quantities of N2O in a plant canopy to constrain the iso-flux of N2O from soils to the atmosphere.