Collaborative Research: Dinitrogen fixation rates and diazotrophic communities in contrasting oxygen regimes of the Eastern Pacific Ocean

合作研究：东太平洋氧状况对比中的二氮固定率和固氮群落

• 批准号: 1356043
• 负责人: Amal Jayakumar
• 金额: $ 34.21万
• 依托单位: Princeton University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-09-01 至 2019-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1356043&HistoricalAwards=false
• 关键词: Collaborative; Research; Dinitrogen; fixation; rates

There are three major open ocean oxygen minimum zones (OMZs) in the world: the Eastern Tropical North Pacific (ETNP), the Eastern Tropical South Pacific (ETSP), and the Arabian Sea. OMZs 
are important areas of denitrification (including anammox) and represent a significant loss 
of fixed nitrogen (N) from the ocean. However, multiple lines of evidence have recently indicated that N inputs via dinitrogen (N2) fixation and denitrification may be more closely coupled in space than previously suggested. Despite the geochemical inferences regarding the location and magnitude of N2 fixation that might be associated with OMZs and the importance of these regions for removing fixed N from the ocean, it is thought that OMZs do not harbour diazotrophs. In a preliminary study, nifH genes and their expression were detected from within the Arabian
 Sea and ETNP OMZs and active N2 fixation was measured in the ETNP OMZ, confirming that N2 fixation occurs in oxygen deficient waters. The PIs propose to measure N2 fixation and the 
diversity of diazotrophic communities with respect to vertical gradients of oxygen, light, 
and dissolved nitrogen (N) concentrations. They will compare these detailed vertical profiles
 with similar profiles made in fully oxic waters adjacent to the OMZs. In addition, they will 
compare and contrast two very different OMZ regions; one that includes some of the most productive oceanic waters on Earth (ETSP), and another that is far less productive (ETNP). As part of
 this project, they will acquire a better understanding of where N2 fixation occurs with respect 
to areas of active denitrification and the microbes involved in these processes. Armed with 
this more comprehensive understanding of the vertical distribution of N2 fixation and active diazotrophic communities with respect to chemical and biological gradients in OMZ waters,
 they will garner a more realistic view of the N cycle within these regions and a better understanding 
of depth-integrated rates of N2 fixation that include oxic and anoxic aphotic waters.Intellectual Merit: Despite the geochemical inferences regarding the location and magnitude of N2 fixation and
its juxtaposition with denitrification within OMZs, there are few rate estimates and biological 
data supporting these conjectures. The biological evidence we do have suggests that diazotrophs are active within the Arabian Sea and ETNP OMZs and that there is measureable N2 fixation 
within the ETNP OMZ. The proposed research will allow the PIs to establish the contribution of diazotrophy to N inventories within and adjacent to two expansive OMZ regions. The ability 
to reconcile oceanic N budgets and construct accurate biogeochemical models is currently limited by the geographical paucity of rate measurements from diverse oceanic environments. In addition, while the PIs have measured active N2 fixation in aphotic waters, they lack the depth resolution 
to include the expansive sub-euphotic oceanic realm in depth-integrated estimates of oceanic 
N2 fixation anywhere. Through their ongoing collaboration with Ward and Devol, who have measured N losses associated with denitrification in this OMZ, the PIs will be able to construct an "end-to-end" view of the N cycle in this globally important system. The molecular data generated from 
this project will not only shed light on the active clades that contribute to oceanic 
N inputs through N2 fixation and N loss through denitrification, but also give insights 
into the relative distributions and activity of diazotophs and dentrifiers along vertical 
gradients of oxygen, light, and dissolved N.Broader Impacts: Results will contribute to our understanding of controls on marine N2 fixation; variations 
in diazotrophy along vertical gradients of light, oxygen, and nutrient concentrations; and
 the balance between N inputs and losses from OMZs. This project will
 be potentially transformative in shaping our view of the oceanic N budget, both the input and output ends. The project will also contribute to education on a number of levels. Undergraduate and graduate students at Old Dominion University and Princeton will have opportunities to gain valuable research experience using state of the art research facilities both on land and at 
sea. In addition, we will create a video classroom to communicate with elementary and middle school students during the cruises to the ETNP and ETSP and keep the scientific community and general public updated through blogs.

世界上有三个主要的开放海洋氧气极小区(OMZ)：东热带北太平洋(ETNP)、东热带南太平洋(ETSP)和阿拉伯海。OMZ&amp；是反硝化作用(包括厌氧氨氧化)的重要区域，是海洋中固定氮(N)的重大损失。然而，最近的多条证据表明，通过氮固定和反硝化作用的氮输入在空间上可能比先前提出的更紧密地耦合。尽管关于氮气固定的位置和大小可能与OMZ有关，以及这些区域对从海洋中清除固定N的重要性，但人们认为OMZ不含有重氮菌。在一项初步研究中，在阿拉伯海和ETNP OMZ中检测到了nifH基因及其表达，并在ETNP OMZ中检测到了活性的氮气固定，证实了在缺氧水域中发生了氮气固定。PIs建议测量相对于氧、光和溶解氮(N)浓度的垂直梯度的氮固定和重氮营养群落的多样性。他们将把这些详细的垂直剖面与在OMZ附近的完全含氧水域制作的类似剖面进行比较。此外，他们还将比较和对比两个截然不同的OMZ地区；一个包括一些地球上生产力最高的海洋水域(ETSP)，另一个生产力低得多的地区(ETNP)。作为这个项目的一部分，他们将更好地了解氮气固定发生在哪里，以及反硝化活跃的区域和参与这些过程的微生物。通过更全面地了解OMZ水域中氮固定的垂直分布和相对于化学和生物梯度的活跃的重氮营养群落，他们将获得这些区域内N循环的更真实的视角，并更好地理解氮固定的深度综合速率，包括缺氧和无氧水。智力价值：尽管关于氮固定的位置和大小及其与OMZ内反硝化作用的并列，很少有速率估计和生物数据支持这些假设。我们有生物学证据表明，重氮菌在阿拉伯海和ETNP OMZ内是活跃的，在ETNP OMZ内有可测量的氮气固定。拟议的研究将使私人投资机构能够确定重氮化对两个扩张的OMZ区域内和邻近的N库存的贡献。目前，由于缺乏来自不同海洋环境的速率测量，协调海洋氮预算和构建准确的生物地球化学模型的能力受到限制。此外，尽管PI测量了无光水域中的活性氮固定，但他们缺乏深度分辨率，无法将广阔的亚真光层海洋领域包括在海洋和任何地方的氮固定的深度综合估计中。通过与Ward和Devol的持续合作，他们测量了与这个OMZ中的反硝化相关的N损失，PI将能够构建这个全球重要系统中N循环的“端到端”视图。这个项目产生的分子数据不仅将有助于揭示通过氮气固定和通过反硝化作用造成氮损失的海洋氮素输入的活跃分支，而且还将使我们深入了解重氮菌和固氮菌在氧、光和溶解氮垂直梯度上的相对分布和活性。布罗德影响：结果将有助于我们理解海洋氮素固定的控制；沿光、氧和营养浓度垂直梯度的重氮化变化；以及。N个输入和来自OMZ的损失之间的平衡。这个项目将潜在地改变我们对海洋N预算的看法，无论是投入还是产出。该项目还将在多个层面上促进教育。老道明大学和普林斯顿大学的本科生和研究生将有机会利用陆上和海上最先进的研究设施获得宝贵的研究经验。此外，我们还将创建一个视频教室，在前往ETNP和ETSP的过程中与中小学生进行交流，并通过博客让科学界和公众了解最新情况。