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Nitrogen Fixation in Deep-Sea Sediments

深海沉积物中的固氮

基本信息

批准号：
1634297
负责人：
Anne Dekas
金额：
$ 39.98万
依托单位：
Stanford University
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 2021-01-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1634297&HistoricalAwards=false
关键词：
Nitrogen Fixation Deep Sea Sediments

项目摘要

Life requires nitrogen for growth. Atmospheric nitrogen (N2) is the most abundant form of nitrogen on the surface of the planet, but most organisms cannot assimilate N2 directly. Habitats can therefore be nitrogen limited, meaning the demand for "bioavailable" nitrogen exceeds the supply, and its availability controls the overall growth and productivity of the community. A small subset of microorganisms, termed diazotrophs, convert N2 to bioavailable forms of nitrogen, including ammonium and nitrogenous organic matter, in a process known as N2 fixation. Diazotrophs are the largest natural source of bioavailable nitrogen on the planet, and the rate at which they fix N2 can control the rates at which other important microbial processes occur, such as the production and consumption of greenhouse gases. Understanding diazotrophs in the environment - their identity, distribution, activity levels, and biogeochemical controls - is therefore essential to understanding overall microbial community activity and biogeochemical cycling. The goal of this project is to characterize N2 fixation in deep-sea sediments, a generally understudied but expansive habitat, covering nearly two thirds of our planet. The project will have broader impacts via educational outreach, support and training of early career scientists, and scientific impact: since rates of marine methane, carbon dioxide, and nitrous oxide cycling are affected by nitrogen availability, the results will inform our understanding of greenhouse gas cycling in the marine environment, and therefore climate stability, a topic central to global security.N2 fixation is a critical and intensely studied metabolism in the marine photic zone. Much less is known about N2 fixation in deep-sea sediments, but it could be an important factor in both benthic productivity and ocean-scale elemental cycling. Several observations have suggested or directly detected N2 fixation at localized areas of enhanced productivity on the seafloor (e.g., methane seeps and hydrothermal vents), raising the possibility that deep-sea N2 fixation is widespread. However, few measurements of N2 fixation have been made outside of these anomalous areas, and thus little is known about N2 fixation in the vast majority of the deep ocean floor. Preliminary data suggest N2 fixation does occur in typical deep marine sediment, and is mediated by a diverse set of yet unidentified microorganisms. This project will combine techniques from molecular biology and geochemistry to systematically investigate N2 fixation in representative deep-sea sediments collected along a depth profile (500 to 4500 m water depth) offshore California. The project will determine the (1) rates and distribution of N2 fixation (2) abundance, diversity, and distribution of genes and transcripts associated with N2 fixation (nif) (3) phylogenetic identity of the biological mediators (diazotrophs) and (4) physiochemical controls on diazotrophic community structure and activity. For context, the activity of the non-diazotrophic bacterial community will also be characterized. The results may lead to upward revisions of the estimates of new nitrogen production in the seafloor, and therefore change our understanding of the current balance of the marine nitrogen cycle. Together, this hypothesis-driven characterization of N2 fixation in deep-sea sediments will shed light on an expansive, climatically important, and traditionally understudied habitat, and facilitate more accurate extrapolation of the rates and distribution of N2 fixation on the whole seafloor as well as the metabolic response of the seafloor community to environmental change.

生命需要氮来生长。大气氮(N2)是地球表面最丰富的氮形式，但大多数生物不能直接同化n2。因此，栖息地可能会受到氮的限制，这意味着对“生物可利用”氮的需求超过了供应，其可获得性控制着群落的整体增长和生产力。一小部分微生物，称为重氮菌，在一个被称为氮气固定的过程中，将氮气转化为生物可利用的氮素形式，包括氨和含氮有机物。重氮菌是地球上生物可利用氮的最大自然来源，它们固定氮气的速度可以控制其他重要微生物过程的发生速度，例如温室气体的生产和消耗。因此，了解环境中的重氮菌--它们的身份、分布、活动水平和生物地球化学控制--对于了解整个微生物群落活动和生物地球化学循环至关重要。这个项目的目标是描述深海沉积物中固定氮气的特征，深海沉积物是一个普遍未被研究但幅员辽阔的栖息地，覆盖了地球近三分之二的地区。该项目将通过教育推广、对早期职业科学家的支持和培训以及科学影响产生更广泛的影响：由于海洋甲烷、二氧化碳和一氧化二氮的循环速率受氮素供应的影响，因此结果将有助于我们了解海洋环境中的温室气体循环，从而了解气候稳定，这是全球安全的核心话题。固定氮气是海洋光区新陈代谢的关键和深入研究。人们对深海沉积物中氮的固定知之甚少，但它可能是底栖动物生产力和海洋尺度元素循环的一个重要因素。一些观测表明或直接探测到在海底生产力提高的局部区域(例如甲烷渗漏和热液喷口)固定氮气，这增加了深海氮气固定普遍存在的可能性。然而，在这些异常区域之外，对氮气固定的测量很少，因此对绝大多数深海海底的氮气固定知之甚少。初步数据表明，氮的固定确实发生在典型的深海沉积物中，并由一组不同的尚未确定的微生物介导。该项目将结合分子生物学和地球化学技术，系统地研究沿加州近海深度剖面(500至4500米水深)收集的具有代表性的深海沉积物中的氮气固定。该项目将确定(1)固氮速率和分布，(2)与固氮相关的基因和转录本的丰度、多样性和分布(NIF)，(3)生物介体(重氮菌)的系统发育特征，以及(4)对重氮营养群落结构和活动的物理化学控制。作为背景，非重氮细菌群落的活性也将被表征。这一结果可能导致向上修正对海底新氮产量的估计，从而改变我们对当前海洋氮循环平衡的理解。总之，这种假设驱动的深海沉积物中氮固定的特征将揭示一个广阔的、气候重要的、传统上研究不足的栖息地，并有助于更准确地推断整个海底的氮固定速率和分布，以及海底群落对环境变化的代谢反应。