太湖典型入湖河流氧化亚氮的微生物还原机制与迁移过程研究

Terrestrial ecosystem nitrogen transported from estuaries to lakes by rivers, the denitrification process in Inflow Rivers has effects on lake nitrogen inputs. Nitrous oxide (N2O) as a strong greenhouse gas has aroused international concern in recent years. As an intermediate product of denitrification process, it can indirectly reflect the denitrification efficiency in aqueous system. N2O reducing bacteria determined the reduction process of N2O to N2, its distribution, activity and environmental factors in lakes and rivers contributed to N2O emission together. Previous studies on N2O in lakes focuses on flux and emission characters, only few research aims at N2O reducing bacteria study. This study will select typical inflow rivers, estuaries and different lake-area of Taihu Lake, investigate the temporal and spatial characteristics of N2O emission, analyze the structure characteristics of N2O reducing bacteria communities, and identifies the key environmental factors which will affect N2O emissions. Secondly, the lab scale membrane aerated bioreactor will be fabricated to immobilize, cultural and separate N2O reducing bacteria, the biokinetic characteristics of N2O reducing bacteria under varies environmental condition will be analyzed. The N2O migration and transformation process at the suspended particle interface in river-lake ecosystem will be analyzed based on molecular biology and stable isotope techniques. Finally, this study will enhance the understanding of key biological process of N2O reduction to N2 and provide scientific basis for the management of N2O emission in river-lake ecosystem.

陆地生态系统中的氮素由河流输运经河口汇入湖泊，入湖河流中的反硝化作用显著影响湖泊氮素输入。氧化亚氮（N2O）是近年来国际广泛关注的强效温室气体，作为反硝化作用中间产物可间接反映水体脱氮效率。N2O还原为N2的关键生物过程由N2O还原细菌决定，其在河流与河湖生态系统中的分布、活性及非生物环境因子共同影响N2O的排放。目前针对河流湖泊N2O的研究侧重于通量与排放特征，对N2O的微生物还原过程研究甚少。本研究选择太湖典型入湖河流、河口及不同特征湖区，调查N2O排放时空特征，分析N2O还原细菌群落结构特征，识别影响N2O排放的关键环境因子；构建室内膜生物反应器富集和分离系统，研究不同环境条件下N2O还原细菌的生物动力学特征；基于分子生物学和稳定同位素技术分析河湖生态系统中悬浮颗粒界面N2O迁移转化过程。加深对河湖生态系统N2O还原成N2关键生物过程的认识，为河湖生态系统管控N2O排放提供科学依据。

陆地生态系统中的氮素由河流输运经河口汇入湖泊，河流反硝化作用影响湖泊氮素输入。目前针对河流湖泊N2O的研究侧重于通量与排放特征，对N2O的微生物还原过程研究甚少。本研究以太湖为主要研究地点，深入分析了太湖典型入湖河流N2O通量变化的微生物作用机制。项目调研了城市、农业入湖河流的N2O排放模式差异；分析了影响N2O排放通量的关键环境因子；高通量测序确定了微生物群落结构差异；解析了不同生境下微生物群落结构差异和N2O排放相关的功能微生物丰度；利用共发生网络分析了N2O排放相关功能微生物与其他微生物之间的竞争和合作关系。在室内进行了N2O还原纯菌的富集、分离、纯化及动力学特征分析。通过野外调查和室内模拟实验，系统阐明了典型入湖河流SPS浓度和粒径特征影响N2O排放的微生物作用机制。研究结果指出：太湖农业区域入湖河流的N2O排放通量显著高于城市区域入湖河流。风速和硝酸盐分别是影响太湖农业和城市入湖河流N2O排放通量的关键因子。nirK型反硝化细菌是城市入湖河流中主导的产N2O微生物，而nirS型反硝化细菌是所有河流底泥中主导的消耗N2O的微生物。构建了藻类浓度与N2O排放通量之间的非线性模式。以醋酸盐为低浓度电子供体时nosZI型N2O还原菌为主导菌，且分离菌株主要为Pseudomonas sp.。碳源浓度增加显著增加了N2O最大还原速率（Vmax）和N2O半饱和常数（Km），N2O功能微生物性质的改变会导致N2O排放通量的差异。本研究加深了对河湖系统N2O还原过程的认识，为河湖生态系统N2O减排提供科学依据。