人类活动使得河口-近岸海域低氧区不断扩大，加速了氮素循环过程，显著提高了N2O的释放通量，导致河口近海成为释放N2O的重要来源。其中反硝化作用是近岸水域N2O排放的一个重要驱动力，但尚不明确其具体的作用机理。推测低氧可能通过调控与反硝化过程N2O产生与消耗相关的功能酶活性，导致N2O的源汇过程不平衡，造成N2O的积累和释放，形成不完全反硝化作用（iDNF）。在低氧条件下，由iDNF产生的N2O占有很大的比重，但目前有关河口-近岸N2O相关的生物地球化学分析中却忽视了这一过程。本项目以珠江口及近海为研究区域，通过氮同位素示踪的方法分析在低氧梯度上iDNF过程对N2O释放通量的贡献，运用分子生态学技术探索低氧对iDNF过程产生和释放N2O的调控机制，并进一步运用微宇宙培养实验验证低氧对促进iDNF过程产生N2O影响。本研究将阐明iDNF在河口近岸海域低氧区N2O释放的作用，揭示其低氧调控机制。

Nitrous oxide (N2O) ranks as the number one ozone-depleting chemical, which is an increasingly important greenhouse gas. Eutrophication of waters has been increasing in many estuarine and coastal areas, leading to very large hypoxia in the affected regions and accelerating the nitrogen cycle process. As a result, the flux of N2O emission was enhanced remarkably. At present, it has been recognized that estuarine and coastal zones were the source of N2O emission to atmosphere. As the marine N2O sources and sinks with complex spatial and temporal patterns of variation, it is not entirely clear microbiological mechanisms in the ocean up currently. Preliminary view that the microbial incomplete denitrification was an important process during reduction of NOx– to N2O by multiple types functional microorganisms. Increased N2O production is probably caused by the addition of anthropogenic nitrate and its subsequent incomplete denitrification, which is favored by hypoxia condition. Hypoxia may regulate the functional enzymes’ activity associated with the production and consumption of N2O in the process of denitrification, leading to an imbalance of source and sink of N2O. At last, N2O would be accumulated and emit to atmosphere. Under low oxygen condition, incomplete denitrification should contribute significantly to the N2O emission. But this process is ignored in the current biogeochemical model of near shore N2O emissions.In this study, we will investigate the microbial mechanism of N2O emission by incomplete denitrification and principle environmental factors impacting this emission in the Pearl River estuary and coastal zones using various methods combined geochemistry to molecular ecology. Firstly, we will analyze the contribution rate of iDNF process to N2O release flux on low oxygen gradient by means of isotope tracer combined with inhibitors. Then, we will explore the regulation mechanism of hypoxia on the production and release of N2O by iDNF process using molecular ecology methods. And furthermore, we will verify the effect of hypoxia on the production of N2O by iDNF process using microcosmic culture experiment. This study would improve the understanding for the fundamental scientific question of the production and release of N2O and building a new biogeochemical model of N2O in hypoxia estuary and coastal zones.