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

世界上有三个主要的开放海洋氧最小带（OMZs）：东热带北太平洋（ETNP）、东热带南太平洋（ETSP）和阿拉伯海。omz, # 8232;是反硝化（包括厌氧氨氧化）的重要领域，并代表重大损失&amp；#8232；来自海洋的固定氮然而，最近的多项证据表明，通过二氮（N2）固定和反硝化的氮输入可能比以前认为的在空间上更紧密地耦合。尽管地球化学推断可能与omz有关的N2固定的位置和大小以及这些区域从海洋中去除固定N的重要性，但人们认为omz不存在重氮营养物。在一项初步研究中，从阿拉伯人&amp；#8232；在ETNP OMZ中测量了海洋和ETNP OMZ以及活跃的N2固定，证实了N2固定发生在缺氧水域。PIs建议测量N2固定度和重氮营养群落在氧、光垂直梯度方面的多样性&amp；#8232；和溶解态氮(N)浓度。他们将比较这些详细的垂直剖面&amp；#8232；在omz附近的全含氧水域也有类似的剖面。此外，他们将&amp；#8232；比较和对比两个非常不同的OMZ区域；一个包括地球上最富生产力的海水（ETSP），另一个则低得多（ETNP）。作为&amp；#8232；在这个项目中，他们将更好地了解N2固定发生在哪里&amp；#8232；主动反硝化区域和参与这些过程的微生物。配备&amp；#8232；更全面地了解OMZ水域氮固定和活性重氮营养群落的垂直分布，以及化学和生物梯度，&#8232；他们将对这些地区的N周期有一个更现实的看法，并更好地理解&amp；#8232；氮固定的深度整合率，包括缺氧和缺氧缺氧水。智力上的优点：尽管地球化学对N2固定的位置和幅度有影响，它与omz内的反硝化并置，很少有速率估计和生物&amp；#8232；支持这些猜想的数据。我们所掌握的生物学证据表明，重氮营养体在阿拉伯海和ETNP omz中很活跃，并且存在可测量的N2固定作用。在ETNP OMZ内。拟议的研究将允许pi确定重氮化对两个扩展的OMZ区域内及其邻近区域的N库存的贡献。能力&amp；#8232；调和海洋氮收支和构建精确的生物地球化学模型目前受到地理上缺乏不同海洋环境速率测量的限制。此外，虽然pi在无光水体中测量了活性N2固定，但它们缺乏深度分辨率。在海洋&amp；#8232；深度综合估计中纳入广阔的亚光海洋领域；N2固定在任何地方。通过与Ward和Devol的持续合作，他们已经测量了与该OMZ中反硝化相关的N损失，pi将能够在这个全球重要系统中构建一个“端到端”的N循环视图。从&amp；#8232；这个项目不仅将揭示对海洋做出贡献的活跃分支；氮的输入通过固氮和氮的损失通过反硝化作用，但也给见解&amp；#8232；重氮石和疏氮剂沿垂直方向的相对分布和活度&amp；#8232；氧、光和溶解氮的梯度。更广泛的影响：研究结果将有助于我们理解海洋氮固定的控制；变化,# 8232;在重氮营养中，沿光、氧和营养浓度的垂直梯度；和安保;# 8232;N个输入和omz损失之间的平衡。这个项目将&amp；#8232；可能会改变我们对海洋N预算的看法，包括投入端和产出端。该项目还将在若干层次上促进教育。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地和海上最先进的研究设施获得宝贵的研究经验。此外，我们将创建一个视频教室，以便在前往ETNP和ETSP的游轮期间与中小学生交流，并通过博客让科学界和公众随时了解最新情况。

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.