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

第1部分：该项目涉及有关硝化作用在南极海洋生态系统中的作用的基本问题(通过涉及两种不同微生物：氨和亚硝酸盐-氧化菌的两步过程将铵转化为硝酸盐)。具体地说，该项目力求评估氮化合物能量支持的初级生产对南大洋食物网有机碳总供应量的贡献。以前的测量表明，硝化作用每年可为支持南极食物网的初级生产贡献约9%，但这些测量不包括与亚硝酸盐氧化有关的额外生产。此外，该项目将致力于确定其他氮源(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。这项工作将有助于更好地了解南极海洋生态系统每年的能量基础，并有助于更好地了解以光能为基础的初级生产有限的时间和地点(即极地夜间或海冰覆盖下)生态系统的能量。该项目将培养一名博士后研究员，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。帕尔默长期生态研究(LTER)的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。相对较少的努力致力于研究与氮循环的微生物地球化学有关的过程，但这是其他LTER地点的一个主要主题。这项工作将大大有助于理解研究区域内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2部分：拟议的工作将量化以铵、尿素和亚硝酸盐形式供应的15N的氧化率，从而能够估计尿素衍生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在黑暗中将14C结合到有机物中的直接测量进行比较，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：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长期环境研究活动将提供一个独特的机会，从整个生态系统的动态--包括初级和次级生产过程--来评估化学自养。

Part 1: The project addresses fundamental questions regarding the role of nitrification (the conversion of ammonium to nitrate by a two-step process involving two different guilds of microorganisms: ammonia- and nitrite-oxidizers)in the Antarctic marine ecosystem. Specifically, the project seeks to evaluate the contribution of primary production supported by the energy in nitrogen compounds to the overall supply of organic carbon to the food web of the Southern Ocean. Previous measurements indicate that nitrification could contribute about 9% to primary production supporting the Antarctic food web on an annual basis, but those measurements did not include the additional production associated with nitrite oxidation. Additionally, the project will aim 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. Such work will aid in better understanding the basis of the energy for the Antarctic marine ecosystems on an annual basis as well as better aid in understanding the energetics of the ecosystem in times and places where primary production based on light energy is limited (i.e. during the polar night or under sea ice cover). 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 Long Term Ecological Research (LTER) 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, yet these are a major themes at other LTER sites. This work will contribute substantially to understanding an important aspect of nitrogen cycling and bacterioplankton production in the 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 the estimation of 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 in 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.