EAGER: Collaborative Research: Detection limit in marine nitrogen fixation measurements - Constraints of rates from the mesopelagic ocean

氮的可用性是支持生活在我们全球海洋表面的生物生长和生产所必需的。这种元素可能是稀缺的。为了缓解这种短缺，一种特殊的细菌和古细菌，称为固氮菌，可以从氮气中获得生长所需的氮。该项目将仔细研究一种测量固氮的具体方法，该方法最近被用来表明在地下海水中存在少量的固氮。如果这些报告得到证实，那么可能需要修订我们对海洋氮循环的理解。海洋碳和生物地球化学项目将作为一个平台，为固氮测量和检测生物多样性、活性和丰度的最佳实践达成共识。此外，将在未来的国家/国际会议上组织一次会议，以便在制定这些最佳做法的同时与更广泛的科学界进行交流。本研究的目的是对中远洋海水中15n2示踪固氮方法固有的潜在实验和分析误差进行彻底检查，并结合全面的分子测量。将在北大西洋的一个巡航样带上收集样本并进行实验工作，然后在实验室进行分析工作。本研究的具体目的是：(1)通过对实验和分析误差来源的表征，确定基于中远洋培养的15N2固定的最小可量化率；(2)通过对相应样品的综合分子方法，寻找固氮基因存在和表达的证据。本研究中测量的可检测率和重氮营养活性的范围将为理解固氮在海洋氮收支中的重要性提供信息。

The availability of nitrogen is required to support the growth and production of organisms living in the surface of our global ocean. This element can be scarce. To alleviate this scarcity, a special class of bacteria and archaea, called nitrogen fixers, can derive the nitrogen needed for growth from nitrogen gas. This project would carefully examine one specific method for measuring nitrogen fixation that has been used recently to suggest the occurrence of small amounts of nitrogen fixation in subsurface ocean waters. If these reports are verified, then a revision of our understanding of the marine nitrogen cycle may be needed. The Ocean Carbon and Biogeochemistry program will be used as a platform to develop community consensus for best practices in nitrogen fixation measurements and detection of diversity, activity, and abundances of the organisms responsible. In addition, a session will be organized in a future national/international conference to communicate with the broader scientific community while developing these best practices.The goal of this study is to conduct a thorough examination of potential experimental and analytical errors inherent to the 15N2-tracer nitrogen fixation method, in tandem with comprehensive molecular measurements, in mesopelagic ocean waters. Samples will be collected and experimental work conducted on a cruise transect in the North Atlantic Ocean, followed by analytical work in the laboratory. The specific aims of this study are to (1) determine the minimum quantifiable rates of 15N2 fixation based on incubations of mesopelagic waters via characterization of sources of experimental and analytical error, and (2) seek evidence of presence and expression of nitrogen fixation genes via comprehensive molecular approaches on corresponding samples. The range of detectable rates and diazotroph activity from the measurements made in this study will be informative for the understanding of the importance of nitrogen fixation in the oceanic nitrogen budget.