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最低含氧区（OMZ）：东热带北太平洋（ETNP），东热带南太平洋（ETSP）和阿拉伯海。OMZs #8232;是反硝化作用（包括厌氧氨氧化）的重要区域，代表了海洋中固定氮（N）的显著损失。然而，最近有多条证据表明，通过二氮（N2）固定和反硝化作用的N输入可能比以前提出的更紧密地耦合在空间。尽管地球化学推断的位置和规模的N2固定，可能与OMZ和这些地区的重要性，从海洋中去除固定N，它被认为是OMZ不窝藏固氮生物。在初步研究中，从阿拉伯#8232;海和ETNP OMZ内检测nifH基因及其表达，并在ETNP OMZ中测量活性N2固定，证实N2固定发生在缺氧沃茨中。PI建议测量N2固定和固氮生物群落的多样性，相对于氧气，光照，溶解氮（N）浓度的垂直梯度。他们将把这些详细的垂直剖面图#8232;与在邻近OMZ的完全含氧沃茨中制作的类似剖面图进行比较。#23232;，&将？比较和对比两个非常不同的OMZ区域;一个包括地球上生产力最高的海洋沃茨（ETSP），另一个生产力低得多（ETNP）。作为#8232;该项目的一部分，他们将更好地了解N2固定发生在#8232;主动反硝化区域和参与这些过程的微生物。#8232;&。这一更全面的了解垂直分布的N2固定和活性固氮菌群落相对于化学和生物梯度在OMZ沃茨，
他们将获得一个更现实的看法，这些地区内的N循环和更好地了解
的深度集成速率的N2固定，包括好氧和缺氧的无光沃茨。智力优点：尽管地球化学推断的位置和规模的N2固定和
它的并列与反硝化作用在OMZ，有几个速率估计和生物
数据支持这些假设。我们所拥有的生物学证据表明，固氮生物在阿拉伯海和ETNP外姆带内是活跃的，并且在ETNP外姆带内有可测量的N2固定。拟议的研究将允许PI建立固氮氮库存内和邻近两个广阔的OMZ区域的贡献。能力
目前，由于地理上缺乏对不同海洋环境中氮素收支的测量，因此，协调海洋氮素收支和建立精确的海洋地球化学模型受到限制。此外，虽然PI已经测量了无光沃茨中的主动N2固定，但他们缺乏深度分辨率，无法将广阔的亚真光海洋领域纳入任何地方海洋N2固定的深度综合估计。通过与沃德和德沃尔的持续合作，他们测量了与该OMZ中反硝化相关的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。从#8232;该项目产生的分子数据&不仅将阐明&通过N2固定和通过反硝化作用的N损失而促进海洋#8232;N输入的活性分支，而且还将深入了解
重氮菌和反硝化菌沿着垂直#8232;的相对分布和活性&。更广泛的影响：结果将有助于我们了解海洋固氮控制;变化
固氮沿着垂直梯度的光，氧和营养浓度;和
 N输入和OMZ损失之间的平衡。该项目将有可能改变我们对海洋氮预算的看法，包括输入端和输出端。该项目还将促进各级教育。在旧自治领大学和普林斯顿大学的本科生和研究生将有机会获得宝贵的研究经验，使用最先进的研究设施在陆地和#8232;海上。此外，我们还将创建一个视频教室，以便在ETNP和ETSP巡航期间与中小学生进行交流，并通过博客向科学界和公众提供最新信息。

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.