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（N2 O）是过去150年来人类活动导致全球变暖的三种最重要的生物源温室气体之一。 因此，N2 O也是温室气体核算做法的一个组成部分，并被纳入欧洲和美国的碳市场（即芝加哥气候交易所）。 虽然IPCC最近的努力平衡了全球N2 O预算，但仍然存在很大的不确定性。 地球上几乎所有的物质在氧的17 O和18 O同位素之间都有一致的关系，称为质量依赖性。 对流层N_2O相对于氧的质量依赖性为0.9？。 N2 O中的17 O异常长期以来被认为反映了平流层中光化学反应的17 O掺入以及平流层和对流层之间的N2 O交换。 最近有人提出，N2 O中的17 O异常是生物产生的，是在微生物产生N2 O的过程中，水中的氧掺入到N2 O中的结果。 如果是正确的，这将是第一次观察到生物产生的17 O异常。 在本提案中，PI将测试三种机制，通过这些机制，17 O异常可能被引入生物产生的N2 O中：（1）与水的交换，（2）来自O2和水的氧的差异结合，以及（3）携带17 O异常的大气硝酸盐的反硝化作用。 此外，他们还将通过无机紫外光氧化测试生产过程中是否存在17 O异常。 PI将采用各种方法来评估生物N2 O产生17 O异常的可能性，包括纯化酶产生N2 O，纯微生物培养和农业土壤的培养。生物产生的N2 O中17 O异常的存在对于理解大气N2 O的起源和国际上对这种重要温室气体的全球收支具有深远的影响。像IPCC这样的组织。 将开发的微生物N2 O生产的仪器，方法和知识将成为MSU短期课程的组成部分，该课程涉及来自全国各地的研究生，教授和专业人士（稳定同位素生物地球化学）。 该项目还将涉及一个团队的本科机械，电气和计算机工程专业的学生谁将开发和部署涡协方差痕量气体捕集系统，这将使收集足够数量的N2 O在植物冠层，以限制N2 O的iso-flux从土壤到大气。

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.