Collaborative Research: Chemoautotrophy in Antarctic Bacterioplankton Communities Supported by the Oxidation of Urea-derived Nitrogen

第1部分：硝化作用是通过两步过程将铵转化为硝酸盐，涉及两种不同的微生物：氨氧化剂和亚硝酸盐氧化剂。这个过程是全球氮循环的核心，影响着从农田肥料的保留到在有害藻类大量繁殖之前从沿海水域去除过量氮的方方面面。它还会产生一氧化二氮，一种破坏臭氧层的温室气体。从两个硝化步骤中获得的能量用于将无机碳转化为微生物生物量。所产生的生物量有助于南大洋食物网的整体生产，并且在冬季低光照水平限制了其他主要生物量来源（单细胞植物的初级生产）时，可能是特别重要的补贴。该项目解决了关于极地海洋生物和地球化学的三个基本问题，重点是硝化过程。该项目将解决的第一个问题是化学自养（基于硝化作用）对南大洋食物网有机碳总体供应的贡献。先前的测量表明，它每年对南极食物网的贡献约为9%，但这些测量不包括与亚硝酸盐氧化相关的额外生产。要解决的第二个问题与第一个问题有关，涉及流程各步骤之间的耦合。第三个目的是确定其他氮源（特别是其他生物体释放的有机氮和尿素）对硝化作用的贡献的重要性，因为这些贡献可能无法通过标准方案进行评估。其他人的测量表明，在极地地区，尿素对硝化作用的重要性可能与铵一样重要。该项目将培养一名博士后研究员，并为本科生提供获得微生物地球化学研究实践经验的机会。Palmer LTER （PAL）活动主要集中在海洋气候与影响顶级捕食者的海洋食物网之间的相互作用。作为帕尔默长期生态研究（LTER）计划的一部分，研究氮循环的微生物地球化学过程的努力相对较少，但这些是其他地点的主要主题。这项工作将大大有助于了解PAL-LTER研究区域氮循环和浮游细菌生产的一个重要方面。该小组将协同工作，充分参与帕尔默LTER的教育和外联工作，包括将调查结果的要点发布在其项目网站上，并参与他们在外联领域的任何特别努力。第二部分：本研究将量化以铵、尿素和亚硝酸盐形式提供的15N的氧化速率，使我们能够估计脲源氮和完全硝化作用（氨到硝酸盐）对南极沿海水域化学自养和浮游细菌生产的贡献。该项目将把这些估计值与直接测量的有机物质中14C的含量进行比较，以独立估计化学自养。该团队的目标是收集跨越水柱的样本：从地表水（~10米），冬季水（50-100米）和环极地深水（150米）；2018年夏天，在一次考察南极半岛西部大陆架和斜坡的巡航中。其他样品将用于测量硝酸盐、亚硝酸盐、氨和尿素的浓度，用于qPCR分析相关微生物的丰度，并用于相关过程的研究。该项目将依靠与现有Palmer LTER的合作，以确保获得辅助数据（浮游细菌丰度和产量、叶绿素、物理和化学变量）。该项目的协同活动以及LTER活动将提供一个独特的机会，在整个生态系统的背景下评估化学自养。S动态-包括初级和次级生产过程。

Part 1: Nitrification is the conversion of ammonium to nitrate by a two-step process involving two different guilds of microorganisms: ammonia- and nitrite-oxidizers. The process is central to the global nitrogen cycle, affecting everything from retention of fertilizer on croplands to removal of excess nitrogen from coastal waters before it can cause blooms of harmful algae. It also produces nitrous oxide, an ozone-destroying, greenhouse gas. The energy derived from both steps of nitrification is used to convert inorganic carbon into microbial biomass. The biomass produced contributes to the overall food web production of the Southern Ocean and may be a particularly important subsidy during winter when low light levels restrict the other major source of biomass, primary production by single-celled plants. This project addresses three fundamental questions about the biology and geochemistry of polar oceans, with a focus on the process of nitrification. The first question the project will address concerns the contribution of chemoautotrophy (based on nitrification) to the overall supply of organic carbon to the food web of the Southern Ocean. Previous measurements indicate that it contributes about 9% to the Antarctic food web on an annual basis, but those measurements did not include the additional production associated with nitrite oxidation. The second question to be addressed is related to the first and concerns the coupling between the steps of the process. The third seeks to determine the significance of the contribution of other sources of nitrogen, (specifically organic nitrogen and urea released by other organisms) to nitrification because these contributions may not be assessed by standard protocols. Measurements made by others suggest that urea in particular might be as important as ammonium to nitrification in polar regions.This project will result in training a postdoctoral researcher and provide undergraduate students opportunities to gain hand-on experience with research on microbial geochemistry. The Palmer LTER (PAL) activities have focused largely on the interaction between ocean climate and the marine food web affecting top predators. Relatively little effort has been devoted to studying processes related to the microbial geochemistry of nitrogen cycling as part of the Palmer Long Term Ecological Research (LTER) program, yet these are a major themes at other sites. This work will contribute substantially to understanding an important aspect of nitrogen cycling and bacterioplankton production in the PAL-LTER study area. The team will be working synergistically and be participating fully in the education and outreach efforts of the Palmer LTER, including making highlights of the findings available for posting to their project web site and participating in any special efforts they have in the area of outreach.Part 2: The proposed work will quantify oxidation rates of 15N supplied as ammonium, urea and nitrite, allowing us to estimate the contribution of urea-derived N and complete nitrification (ammonia to nitrate) to chemoautotrophy and bacterioplankton production in Antarctic coastal waters. The project will compare these estimates to direct measurements of the incorporation of 14C into organic matter the dark for an independent estimate of chemoautotrophy. The team aims to collect samples spanning the water column: from surface water (~10 m), winter water (50-100 m) and circumpolar deep water (150 m); on a cruise surveying the continental shelf and slope west of the Antarctic Peninsula in the austral summer of 2018. Other samples will be taken to measure the concentrations of nitrate, nitrite, ammonia and urea, for qPCR analysis of the abundance of relevant microorganisms, and for studies of related processes. The project will rely on collaboration with the existing Palmer LTER to ensure that ancillary data (bacterioplankton abundance and production, chlorophyll, physical and chemical variables) will be available. The synergistic activities of this project along with the LTER activities will provide a unique opportunity to assess chemoautotrophy in context of the overall ecosystem?s dynamics- including both primary and secondary production processes.