Dimensions: Diversity, assembly and function of microbial communities on suspended and sinking particles in a marine Oxygen Deficient Zone

海洋缺氧区(ODZ)是指功能上缺乏氧气的水域。在没有氧气的情况下，一些微生物能够将水中的氮转化为氮气，然后氮气离开海洋进入大气。海洋中一种重要营养物质的丧失对浮游植物的生长和海洋食物网产生了影响。虽然缺氧区只占海洋的很小比例，但它们占海洋N的损失的比例高达N_2的一半。此外，由于气候变化，这些地区的规模预计将在本世纪扩大。能够产生氮气的微生物极其多样化，并使用几种不同的生化途径来实现这一过程。它们既可以自由漂浮在水中，也可以附着在悬浮或从地表水域下沉的小颗粒上，为它们提供碳源。然而，就海洋氮损失的贡献而言，这两种生活方式(自由生活和附着颗粒)的重要性还没有得到很好的理解。该项目将确定导致悬浮颗粒和下沉颗粒产生氮气的主要生物，它们进行的化学反应，以及发生这种反应的速度。这些信息将被用来改进全球气候模型，以更好地预测未来海洋中N的损失速度。参加科学教师科学硕士项目的中小学教师将参与该项目，该项目支持的研究生和博士后研究人员将有机会参与他们的课堂。服务不足的人群还将通过一系列暑期实习纳入本科和中学层面的研究。ODZ具有非常复杂的元素周期，意味着巨大的微生物多样性。与ODZ区域的微生物复杂性交织在一起的是自由生活的细菌和那些生活在悬浮或下沉颗粒上的细菌之间相对未被探索的相互作用。确定这些群落和生态位如何相互作用和联系是当今ODZ系统研究中最具挑战性的组成部分之一。目前的气候模型通过基于来自含氧海洋的稀疏数据的规定函数，描绘了臭氧管制区和整个深海中颗粒的动态，微生物仅由群落的净化学反应表示。然而，实际上，一群在系统发育和代谢上不同的微生物，很可能是以联合体的方式行动，负责最终导致氮气产生的氮素转化。为了探讨氮损失过程中维持遗传多样性和功能冗余的过程，将综合四个研究领域：群落系统发育多样性(分类学和基因组多样性)、执行关键氮转化过程的蛋白质的遗传多样性(通过定量蛋白质组学观察)、由此产生的生物地球化学功能(15N标记的氮转化速率测量)以及关于这种多样性和相应功能可能如何随着气候变化而变化的预测(生物地球化学建模)。该方法将对使用大容量沉积物捕捉器收集的下沉颗粒进行系统进化(16S rRNA标签测序)和功能遗传多样性(基因组学)分析。系统发育和基因组研究将与活动的测量密切相关--谁在进行关键的生物地球化学转化(蛋白质组学)，以及他们进行转化的原位速率是多少(使用新的孵化系统)。然后，数据将被用来模拟多样性和相应的功能如何在一系列时间和空间尺度上变化，从单个颗粒的下沉到季节性周期。为了解悬浮物和沉降物的群落多样性与功能的关系，将在东热带北太平洋ODZ进行一系列的三次巡航。

Marine oxygen deficient zones (ODZs) are waters that are functionally devoid of oxygen. Without oxygen, some microbes are capable of converting nitrogen in the water into N2 gas, which then leaves the ocean and enters the atmosphere. This loss of an important nutrient from the ocean has impacts on phytoplankton growth and marine food webs. While oxygen deficient zones occupy a very small percentage of the ocean, they account for as much as half of the oceanic loss of N as N2. Moreover, the size of these regions is predicted to expand during this century due to climate change. The microbes that are capable of producing N2 gas are extremely diverse, and use several different biochemical pathways to carry out this process. They may occur both free-floating in the water and attached to small particles that are suspended or sinking from the surface waters and providing them a carbon source. However the importance of these two lifestyles (free-living vs particle attached) in terms of contributions to N loss from the oceans is not well understood. This project will identify the major organisms that result in N2 gas production on both suspended and sinking particles, the chemical reactions they carry out, and the rates at which this occurs. This information will be used to improve global climate models to better predict rates of N loss in a future ocean. Elementary and middle school teachers enrolled in a Masters in Science for Science Teachers program will be involved in the project and the graduate students and post-doctoral researchers supported by the project will have opportunities to participate in their classrooms. Underserved populations will also be integrated into the research at the undergraduate and middle school level through a series of summer internships.ODZs have very complex elemental cycles, implying great microbial diversity. Intertwined with the microbial complexity of ODZ regions is the relatively unexplored interplay between free-living bacteria and those living on either suspended or sinking particles. Determining how these communities and niches interact and relate is one of the most challenging components of ODZ system studies today. Current climate models portray the dynamics of particles in the ODZs and throughout the deep ocean through prescribed functions based on sparse data from the oxic ocean with microbes represented only by the net chemical reactions of the community. However, in reality a phylogenetically and metabolically diverse group of microbes, likely acting in consortia, are responsible for the nitrogen transformations that ultimately result in the production of N2. To explore the processes maintaining the genetic diversity and functional redundancy in N loss processes, four research areas will be integrated: the community phylogenetic diversity (both taxonomic and genomic diversity) the genetic diversity of the proteins that carry out key N transformation processes (as seen through quantitative proteomics), the resulting biogeochemical functions (15N labeled nitrogen transformation rate measurements) and predictions about how this diversity and corresponding function may change in response to climate change (biogeochemical modeling). The approach will be to assay both phylogenetic (16S rRNA tag sequencing) and functional genetic diversity (genomics) on sinking particles collected using large-volume sediment traps. Phylogenetic and genomic studies will be intimately tied to measurements of activity - who is doing key biogeochemical transformations (proteomics) and what are the in situ rates at which they are doing them (using novel incubation systems). Data will then be used to model how diversity and corresponding function change on a range of time and space scales, from the sinking of a single particle to seasonal cycles. To understand the relationship of community diversity and function on suspended and sinking particles, a series of three cruises will be conducted in the Eastern Tropical North Pacific ODZ.