活性氮超负荷是河口生态系统面临的最严重生态环境问题之一，约50%输入的活性氮会通过微生物代谢过程转化成氮气等排入大气，显著降低了河口的富营养化水平，促进氮素循环平衡。尽管认识到这一过程在氮素生物地球化学转化中重要性，但目前对其具体的作用机制还没有深入了解。本项目以典型亚热带河口珠江口为模式，运用地球化学、微生物分子生态学以及实验室模拟原位培养的交叉技术手段，从硝化-反硝化-厌氧氨氧化耦合的创新研究思路，分析与氮转化相关的重要微生物功能群在珠江口水体和沉积物中的时空分布、多样性、丰度及活性特征，探索跨珠江口物理化学梯度以及季节变换等环境因素对微生物过程的影响，研究微生物代谢过程在脱氮过程中的作用。依此构建河口"微生物氮泵"的脱氮机制模型，阐明其分子和生物地球化学的科学内涵及其生态功能。研究结果将为更深入理解河口微生物脱氮机制提供理论基础，同时为揭示人类活动对河口脱氮过程的影响提供科学依据。

Although nitrogen (N) acts as a limiting nutrient in many marine ecosystems, N in excess can be extremely detrimental.Harmful levels of N in estuaries can be diminished through tightly coupled processes in the microbial nitrogen cycle, including nitrification denitrification and Anammox. In fact, coupled nitrification,denitrification to Anammox can remove up to 50% of external dissolved inorganic nitrogen inputs to estuaries, thereby reducing the risk of eutrophication. Despite the biogeochemical importance of both nitrification and denitrification in estuarine systems, surprisingly little is known regarding the underlying microbial communities responsible for these processes, or how they are influenced by key physical/chemical factors. .The investigators will work in Pear River Estuary - the largest estuary on the south coast of the China - using molecular, biogeochemical and cultivation approaches to explore how the distribution, diversity, abundance, and activities of key N-cycling communities and the influence by environmental gradients over temporal and spatial scales. Denitrifying and Anammox communities will be studied using functional genes (nirK and nirS for denitrification, AnirS for Anammox) encoding the key enzyme nitrite reductase, while genes encoding ammonia monooxygenase subunit A (amoA) will be used to study both ammonia-oxidizing bacteria (AOB) and the recently-discovered ammonia-oxidizing archaea (AOA)- members of one of the most ubiquitous and abundant prokaryotic groups on the planet, the mesophilic Crenarchaeota. Analyzing water and sediments from sites spanning a range of physical and chemical conditions in the Estuary, seasonally over the course of several years, will represent an unprecedented opportunity to examine spatial, physical/chemical, and temporal effects on both denitrifier,ammonia-oxidizer and anammoxer communities in this large, urban estuary. Concurrently, an intensive cultivation effort will also be undertaken, in order to get novel funtional culture collections. Taken together, these complimentary approaches will help build a model of "microbial nitrogen pump",which could reveal the mechanism of nitrogen removal by microbal process and its ecological effect. The impacts include obtaining a critical understanding of how underlying N-cycling microbial communities are influenced by complex and fluctuating environmental gradients over time and space in the estuary, which should translate to insights into the ecology and regulation of these biogeochemically-important processes in all estuarine systems.