Using experiments and stable isotopes to track the fate of fixed nitrogen in the marine environment

**0*0*1*429*2448*MIT/WHOI*20*5*2872*14.0***正常*0***FALSE**EN-US*JA*X-NONE******/**样式定义*/*表。MsoNormal表*{mso-style-name：“表正常”；*mso-tstyle-rowband-size：0；*mso-tstyle-colband-size：0；*mso-style-noshow：yes；*mso-style-first：99；*mso-style-Parent：“”；*mso-pding-alt：0in 5.4pt 0in 5.4pt；*mso-para-mark-top：0in；*mso-para-mark-top：0in；*mso-para-mark-Bottom：10.0pt；*mso-para-边距-Left：0in；*mso-Page：寡妇-孤儿；*字体大小：12.0pt；*字体-家族：寒武纪；*mso-ascii-font-家族：寒武纪；*mso-ascii-主题-字体：小拉丁语；*mso-hansi-font-Family：寒武纪；*mso-hansi-主题-字体：小拉丁语；*mso-fareast-Language：Ja；*氮*对地球上的所有生命都是必不可少的。在海洋中，氮通常是限制营养物质，控制初级生产力，从而控制从大气中吸收二氧化碳。虽然氮对生命很重要，但过量的氮也可能有害。在沿海水域，氮作为农业和废水流失的污染物加入，进而导致藻类大量繁殖，当藻类死亡并被微生物呼吸时，这些微生物消耗水柱中的氧气，形成“死区”，在那里动物无法生存。人类通过将地球上的固定氮量增加一倍来制造这些“死区”(格鲁伯和加洛韦，2008)。环境中营养物质的增加也可以刺激微生物产生N2O。N2O是一种温室气体，其威力是二氧化碳的200倍，因此限制N2O的来源对于理解气候变化非常重要。微生物是海洋中氮的一个整体控制器；一些微生物通过将氮气转化为生物质来自然地添加固定的氮；另一些微生物可以通过反硝化和厌氧氨氧化将其去除*回到气态。随着未来人类对环境的改变，了解这些微生物将如何应对和抵消富营养化的负面影响将是当务之急。在我的研究计划中，我有一个培养设施，它将*培养氮循环微生物，以便回答有关微生物如何对沿海营养物质负荷或气候变化等人为影响做出反应的关键问题。*我在研究中使用的主要工具是稳定同位素。亚硝酸盐和硝酸盐的氮(N)和氧(O)同位素可以一起用于解开共生的海洋生物地球化学过程。成功使用任何稳定的*同位素特征取决于对关键微生物过程的同位素系统学*的深入了解。目前，缺乏这些基本信息是在大多数海洋生物地球化学系统中成功利用自然丰度稳定同位素的主要障碍。我的研究计划的主要目标*是确定自然丰度稳定的同位素在哪里可以用来回答复杂的生物地球化学和环境重要问题，并*开发必要的框架来利用它们。*该计划的预期好处将是：1)加深对微生物氮循环过程的复杂性的了解；2)这些过程的稳定同位素系统；3)一个明确定义的计划，使用氮和氧稳定同位素作为监测沿海环境和水产养殖中氮的一种方式，以保护当地水域不受未来气候和人类活动的影响。

* * 0* 0* 1* 429* 2448* MIT/WHOI* 20* 5* 2872* 14.0* * * * *** * Normal* 0* * * * * false* false* false* * EN-US* JA* X-NONE* * * * * * * * * * * * * * * * * * * * * * * * * ** * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *** **** /* Style Definitions */*table.MsoNormalTable* {mso-style-name:"Table Normal";* mso-tstyle-rowband-size:0;* mso-tstyle-colband-size:0;* mso-style-noshow:yes;* mso-style-priority:99;* mso-style-parent:"";* mso-padding-alt:0in 5.4pt 0in 5.4pt;* mso-para-margin-top:0in;* mso-para-margin-right:0in;* mso-para-margin-bottom:10.0pt;* mso-para-margin-left:0in;* mso-pagination:widow-orphan;* font-size:12.0pt;* font-family:Cambria;* mso-ascii-font-family:Cambria;* mso-ascii-theme-font:minor-latin;* mso-hansi-font-family:Cambria;* mso-hansi-theme-font:minor-latin;* mso-fareast-language:JA;}****Nitrogen*is essential for all life on this planet. In the ocean nitrogen is often the*limiting nutrient, controlling primary production and consequently carbon dioxide*uptake from the atmosphere. While nitrogen is important for life, it can also*be harmful in excess. In coastal waters nitrogen is added as a pollutant from*agriculture and wastewater run off, which in turn causes blooms of algae, which*when they die and are respired by microbes that consume oxygen from the water*column creating “dead zones,” where no animal can survive. Humans have created*these “dead zones” by doubling the amount of fixed nitrogen on the planet (Gruber*and Galloway, 2008). Increased nutrients in the environment can also stimulate*microbially mediated N2O production. N2O is a greenhouse*gas 200 times more potent than carbon dioxide, so constraining this source is*important for understanding climate change. ******Microbes are an integral controller of nitrogen in the ocean; some add fixed*nitrogen naturally by turning nitrogen gas into biomass; others can remove it*back to its gaseous form through denitrification and anammox. With future human*induced changes to the environment it will be imperative to understand how*these microbes will respond and counteract the negative impacts of*eutrophication. In my research program, I have a culture facility that will*grow nitrogen cycling microbes in order to answer over-arching questions on how*microbes can respond to anthropogenic influences such as coastal nutrient*loading or climate change. ******The main tools I use in my research are stable isotopes. The nitrogen (N) and*oxygen (O) isotopes of nitrite and nitrate can be used together to disentangle*co-occurring marine biogeochemical processes. The success of using any stable*isotope signature depends on an in depth understanding of isotope systematics*for key microbial processes. The lack of this basic information is currently*the major roadblock to successfully using natural abundance stable isotopes in*most marine biogeochemical systems. The major objectives of my research program*are to identify where natural abundance stable isotopes can be useful for*answering complex biogeochemical and environmentally important questions and to*develop the necessary framework for utilizing them. ******The anticipated benefits of this program will be 1) an increased understanding*of the complexity of microbial nitrogen cycling processes, 2) the stable*isotope systematics of these processes, and 3) a clearly defined plan for using*nitrogen and oxygen stable isotopes as a way to monitor nitrogen in the coastal*environment and aquaculture, in order to protect local waters from future*climate and anthropog