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Collaborative Research: Predicting controls of partitioning between dissimilatory nitrate reduction to ammonium (DNRA) and dinitrogen production in marine sediments

合作研究：预测海洋沉积物中异化硝酸盐还原成铵（DNRA）和氮生成之间的分配控制

基本信息

批准号：
1635461
负责人：
Jeremy Rich
金额：
$ 47.98万
依托单位：
University of Maine
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2016
资助国家：
美国
起止时间：
2016-09-01 至 2021-08-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1635461&HistoricalAwards=false
关键词：
Collaborative Research Predicting controls partitioning

项目摘要

Microbial processes in marine sediments play a major role in the global nitrogen cycle. Because the presence of nitrogen compounds dissolved in seawater largely controls biological growth, understanding how the sedimentary nitrogen budget changes with altered circulation, acidity, and biological productivity is of critical importance to predict oceanic function in future climate scenarios. Surprisingly, we do not know definitively if nitrogen exchange between sediments and the water column is in balance, and if not, how it varies over time and space. We do know that two bacterially mediated chemical reactions are primarily responsible for removing nitrogen from marine ecosystems by converting biologically usable forms of dissolved nitrogen back to nitrogen gas (N2) that is not generally available for biological production. These reactions are called denitrification and anaerobic ammonium oxidation (anammox); the latter operating only where oxygen is zero. This project will investigate a third reaction, called dissimilatory nitrate reduction (DNRA), which competes directly with anammox to limit N2 production and the consequent "loss" of nitrogen, thus retaining nitrogen for use in marine ecosystems. The role of DNRA has not been fully explored and quantifying this reaction could help evaluate the overall nitrogen balance in ocean systems. The researchers here will use novel experimental reactors that contain collected marine sediments and, by varying environmental conditions (pH, temperature, oxygen, organic carbon), will discover and quantify what controls rates of DNRA, denitrification, and anammox in sediments. This will provide a direct test and further development of theoretical sedimentary nitrogen models that can be used to predict possible changes in the global nitrogen cycle resulting with various future climate scenarios. Two graduate students will participate in the research and collaborations with the Maine Coastal Observing Alliance (MCOA) and the Gulf of Maine Institute (GOMI), as well as the Institute for Broadening Participation (IBP) will generate minority student involvement and enhanced outreach activity.This project uses thermodynamic calculations and empirical evidence as a basis to evaluate the ratio of available organic carbon (C) to nitrate (NO3-) as a key controlling factor of nitrogen redox partitioning; with higher ratios believed to favor dissimilatory nitrate reduction (DNRA) over N2 production. The investigator's theoretical model predicts rapid and reversible transitions between DNRA and N2 production over relatively small changes in C/NO3-. This suggests that partitioning could be sensitive to seasonal and possibly inter-annual differences in organic C deposition as well as processes that control nitrate flux to the sediments such as water column stratification. Quantitative relationships between sedimentary C/NO3- and nitrogen partitioning remain poorly defined, and a number of other factors including T, H2S, and Fe(II), are known to influence N partitioning. This study will investigate the hypothesis that relationships between nitrogen redox partitioning and C/NO3-, and by extension H2S/NO3-, are predicted by the proposed theoretical sedimentary nitrogen model. Experiments will varying NO3 fluxes while providing hydrogen sulfide (H2S) and 13C-labelled detritus as electron donors, and measure transformation rates of 15NO3- to 15NH4+ and 29/30N2 in thin disc reactors to determine rates and pathways of DNRA and N2 production. The proposed integration of these experiments with a theoretically-based biogeochemical model will develop a quantifiable and testable understanding of the marine nitrogen cycle. This study should provide a major advance that could be broadly applied to quantitatively predict the sedimentary balance between nitrogen retention and loss across marine ecosystems.

海洋沉积物中的微生物过程在全球氮循环中起着重要作用。由于溶解在海水中的氮化合物的存在在很大程度上控制着生物的生长，因此了解沉积氮收支如何随着循环、酸度和生物生产力的改变而变化，对于预测未来气候情景中的海洋功能至关重要。令人惊讶的是，我们并不确切地知道沉积物和水柱之间的氮交换是否平衡，如果不平衡，它如何随时间和空间而变化。我们确实知道，两种细菌介导的化学反应主要负责从海洋生态系统中去除氮，将生物可用形式的溶解氮转化为生物生产通常无法获得的氮气（N2）。这些反应被称为反硝化和厌氧氨氧化（anammox）;后者仅在氧气为零的情况下运行。该项目将研究第三种反应，称为异化硝酸盐还原（DNRA），它与厌氧氨氧化反应直接竞争，以限制N2的产生和随之而来的氮的“损失”，从而保留氮用于海洋生态系统。DNRA的作用尚未得到充分探讨，量化这种反应可能有助于评估海洋系统中的整体氮平衡。这里的研究人员将使用含有收集的海洋沉积物的新型实验反应器，通过改变环境条件（pH值，温度，氧气，有机碳），将发现并量化沉积物中DNRA，反硝化和厌氧氨氧化速率的控制因素。这将提供一个直接的测试和进一步发展的理论沉积氮模型，可用于预测全球氮循环的可能变化，导致各种未来的气候情景。两名研究生将参与研究和与缅因州海岸观测联盟（MCOA）和缅因州湾研究所（GOMI）的合作，以及扩大参与研究所（IBP）将产生少数民族学生的参与和加强外展活动。该项目使用热力学计算和经验证据作为基础，以评估有效有机碳（C）与硝酸盐（NO3-）的比例。作为氮氧化还原分配的关键控制因素;据信较高的比率有利于异化硝酸盐还原（DNRA）而不是N2生产。研究人员的理论模型预测了DNRA和N2生产之间的快速和可逆的转变，C/NO3-的变化相对较小。这表明，分区可能是敏感的季节性和可能的年际差异，有机碳沉积以及控制硝酸盐通量的沉积物，如水柱分层的过程。沉积物C/NO3-和氮分配之间的定量关系仍然很难定义，和一些其他因素，包括T，H2S，和Fe（II），是已知的影响N分配。本研究将探讨氮氧化还原分配和C/NO3-之间的关系，并通过扩展H2S/NO3-，所提出的理论沉积氮模型预测的假设。实验将改变NO3通量，同时提供硫化氢（H2S）和13 C-标记的碎屑作为电子供体，并在薄圆盘反应器中测量15 NO3-到15 NH 4+和29/30 N2的转化率，以确定DNRA和N2生产的速率和途径。这些实验与基于理论的海洋地球化学模型的拟议整合将发展一个可量化和可测试的海洋氮循环的理解。这项研究应该提供一个重大的进步，可以广泛应用于定量预测氮的保留和损失之间的沉积平衡在海洋生态系统。