Environmental control of microbial N20 fluxes and DIN loss in salt marsh sediments

一氧化二氮(N2O)被列为头号臭氧消耗化学品(篡夺已被《蒙特利尔议定书》成功控制的氯氟烃)，是一种日益重要的温室气体。理解和控制N2O的通量是复杂的，因为它是由自然系统产生的，也是由干扰这些自然系统的人类活动产生的。最重要的扰动之一是，由于化石燃料燃烧和化肥使用的综合影响，生物圈中固定氮(N)的数量急剧增加。大部分多余的氮被施于陆地并释放到大气中，最终进入河口和沿海水域，导致这些栖息地的生态发生了根本性的重组。盐沼是沿海景观的基本特征，沼泽沉积物中的微生物过程对陆地和海洋之间的氮素交换至关重要。这项研究将考察两个关键环境变量--氮素供应和氧化还原条件--对盐沼中N2O和氮气通量的影响。这项工作将在马萨诸塞州的一片沼泽中进行，那里一直是一项长期进行的施肥实验的地点，在这项实验中，不同的氮素被添加到不同的试验点已经有30年了。将使用分子生物学方法，利用对N2O产生、硝化和反硝化作用具有诊断作用的功能基因来检测微生物群落的组成、活性和丰度。速率测量和基因分布/表达分析将检查氮供应和氧化还原条件如何独立影响每个位置产生的N2O和N2的比例以及负责该产生的途径。这项研究将提高我们对负责氮循环的关键微生物的活动、与这些微生物相关的气态氮通量以及调节两者的环境因素之间的相互作用的理解。在这项研究的同时，还提出了推广和教育的三个组成部分：(1)改进普林斯顿大学环境科学的本科课程，(2)提高公众对微生物学在维持全球盐沼和氮循环中所起作用的认识，以及(3)培训下一代微生物生态学研究人员。在普林斯顿大学，首席研究员(Ward)教授普林斯顿环境研究所环境科学导论课程中的一门核心课程。这位Copi(Bowen)将于2010年秋天开始她在波士顿马萨诸塞大学的教学生涯，并将把这项研究纳入她的新课程。沃德和鲍文将能够为本科课程开发体验式学习机会，这些课程是在这项研究的基础上有机发展起来的。此外，还将开发一个新的网站，以提供有关该项目的目标和进展的信息，教育公众有关施肥对沿海生态系统的影响，以及湿地，特别是其中的微生物在维持河口和沿海水域的生产力方面所发挥的关键作用。最后，两个专业人员将作为一个团队，将不同社会经济和文化背景的年轻研究人员带入现场和实验室，进行实践研究，包括课堂项目中的本科生，初级和高级论文研究项目，以及研究生，他们的论文研究将是该项目的一部分。

Nitrous oxide (N2O) ranks as the number one ozone-depleting chemical (usurping chloroflorocarbons, which have been successfully controlled by the Montreal Protocol) and is an increasingly important greenhouse gas. Understanding and controlling the flux of N2O is complicated because it is produced by natural systems as well as by human activity that perturbs these natural systems. One of the most important perturbations is the dramatic increase in the amount of fixed nitrogen (N) in the biosphere through the combined effect of fossil fuel combustion and fertilizer application. Much of the excess N applied on land and released to the atmosphere eventually finds it way to estuarine and coastal waters, leading to a fundamental restructuring of the ecology of these habitats. Salt marshes are an essential feature of coastal landscapes and microbial processes in marsh sediments are critical to the exchange of nitrogen between land and sea. The research proposed here will examine the effects of two key environmental variables, N supply and redox conditions, on the fluxes of N2O and N2 in salt marshes. The work will be performed at a marsh in Massachusetts that has been the site of a long running fertilization experiment, in which varying amounts of nitrogen have been added to different test sites for 30 years. Molecular biological methods will be used to examine the microbial community composition, activity and abundance using functional genes that are diagnostic for N2O production, nitrification and denitrification. Rate measurements and gene distribution/expression analyses will examine how N supply and redox conditions independently affect the proportion of N2O and N2 produced at each site and the pathways that are responsible for that production.This research will improve our understanding of the interaction between the activity of key microorganisms responsible for nitrogen cycling, the gaseous N fluxes associated with those microorganisms, and the environmental factors that regulate both. Three components of outreach and education are proposed in parallel with the research: (1) improve undergraduate curriculum in environmental science at Princeton, (2) increase public awareness of the role that microbiology plays in the maintenance of salt marshes and cycling of nitrogen globally, and (3) train the next generation of microbial ecology researchers. At Princeton University, the lead investigator (Ward) teaches one of the core courses in the Princeton Environmental Institute's Introduction to Environmental Science courses. The CoPI (Bowen) will be starting her teaching career at University of Massachusetts, Boston, in the fall of 2010, and will incorporate this research into her new courses. Both Ward and Bowen will be able to develop experiential learning opportunities for undergraduate courses that grow organically out of this research. In addition a new web site will be developed to provide information on the project's goals and progress, educate the public about the impact of fertilization on coastal ecosystems, and the critical role that wetlands and, particularly, the microbes that reside therein, play in maintaining the productivity of estuarine and coastal waters. Finally both PIs will work as a team to bring socioeconomically and culturally diverse young investigators into the field and laboratory to perform hands-on research that will include undergraduates in class projects, and junior and senior thesis research projects, and graduate students, whose dissertation research will be a part of this project.