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

为了支持生活在我们全球海洋表面的生物的生长和生产，氮的供应是必需的。这种元素可能是稀缺的。为了缓解这种稀缺性，一种特殊的细菌和古细菌可以从氮气中获得生长所需的氮，这种细菌和古生菌被称为固氮菌。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洋水域中发生了少量的固氮。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计划将作为一个平台，在固氮测量和检测相关生物的多样性、活性和丰度方面形成社区共识。此外，还将在今后的一次国家/国际会议上组织一次会议，与更广泛的科学界交流，同时制定这些最佳做法。这项研究的目标是彻底检查15N-示踪剂固氮方法在中层海洋水域的潜在实验和分析误差，同时进行全面的分子测量。将在北大西洋的一个邮轮横断面上采集样本并进行实验工作，然后在实验室进行分析工作。这项研究的具体目的是(1)通过表征实验和分析误差的来源，确定基于中层水域孵化的15N_2固定的最小可量化速率，以及(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。这项研究中测量的可检测速率和重氮菌活性的范围将有助于理解固氮在海洋氮收支中的重要性。

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.