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

第一部分：硝化作用是通过两个不同的微生物群：氨氧化菌和亚硝酸氧化菌，通过两步过程将铵转化为硝酸盐。这一过程是全球氮循环的核心，影响着从农田保留化肥到在可能导致有害藻类大量繁殖之前从沿海水域清除多余氮素的方方面面。它还会产生一氧化二氮，一种破坏臭氧的温室气体。这两步硝化作用产生的能量被用来将无机碳转化为微生物生物质。所生产的生物量对南大洋的整个食物网生产作出贡献，在冬季，当低光照限制了生物量的另一个主要来源--单细胞植物初级生产时，生物量可能是一种特别重要的补贴。该项目涉及关于极地海洋的生物和地球化学的三个基本问题，重点是硝化作用的过程。该项目将解决的第一个问题涉及化学自养(基于硝化作用)对南大洋食物网有机碳总供应量的贡献。以前的测量表明，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有关的额外产量。要解决的第二个问题与第一个问题有关，涉及该进程各步骤之间的耦合。第三项旨在确定其他氮源(特别是其他生物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，尿素在极地地区的硝化作用中可能与铵一样重要。该项目将培养一名博士后研究人员，并为本科生提供在微生物地球化学研究方面获得实践经验的机会。Palmer LTER(PAL)活动主要集中在影响顶级捕食者的海洋气候和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，对氮循环微生物地球化学过程的研究相对较少，但这些是其他地点的一个主要主题。这项工作将大大有助于理解PAL-LTER研究区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，全面参与Palmer LTER的教育和外联工作，包括重点介绍可在其项目网站上公布的研究结果，并参与他们在外展领域所做的任何特别努力。第二部分：拟议的工作将量化以铵、尿素和亚硝酸盐形式提供的15N的氧化率，使我们能够估计尿素衍生N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与直接测量14C在黑暗中有机物质中的结合进行比较，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：地表水(~10米)、冬季水(50-100米)和环极深水(150米)；2018年南极洲夏季乘坐邮轮调查南极半岛以西的大陆架和斜坡。其他样本将用于测量硝酸盐、亚硝酸盐、氨和尿素的浓度，用于相关微生物丰度的定量聚合酶链式反应分析，并用于相关过程的研究。该项目将依靠与现有Palmer LTER的合作，以确保将获得辅助数据(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-包括一次和二次生产过程。

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.