微生物驱动的河流生态系统氮循环过程及其耦合

河流生态系统生境复杂多样，生活着数量巨大、类群众多的微生物，参与和调控氮素在不同形态（如铵态氮、亚硝态氮、硝态氮等）间转化的氮循环过程，但我们缺乏对微生物驱动下河流氮循环关键过程及其耦合的认知。本项目结合野外取样、实验室测定和数据分析，揭示河流沉积物氮循环关键过程（包括固氮、硝化、反硝化、厌氧氨氧化、硝酸盐异化还原成铵）时空格局及主要生态环境影响因子；运用宏基因组/转录组测序和实时定量PCR技术及微宇宙实验，分析参与关键氮循环过程微生物的相应酶编码基因（nifH；amoA；nirK/nirS/nosZ；hzsA；nrfA）多样性，量化微生物群落结构及其功能基因丰度与氮循环关键过程之间的关系；进而从微生物多样性及其关键酶编码基因表达、以及氮循环过程中各氮转化途径间底物和产物关联的视角，探索微生物驱动下河流生态系统氮循环关键过程间的耦合机制，为恢复河流生物多样性和提升生态服务功能提供科学依据。

A riverine network can be viewed as an open ecosystem interlinked longitudinally, laterally, and vertically by hydrologic processes, and it also serves as biogeochemical cycle pathway for C, N and other biogenic elements among the terrestrial, atmospheric and marine ecosystems. Since the industrialization for the past one and half century, human activities have led to a significant increase in bioactive nitrogen concentration in rivers, resulting increasing eutrophication, and impaired biodiversity integrity and ecosystem service in the river ecosystem. On the other hand, the riverine ecosystems provide diverse habitats for numerous organisms which include a large number of microbials with diverse and unique genetic and metabolic variabilities. Among their numerous functions in maintaining health riverine ecosystems, microbials participate in and essentially regulate nitrogen cycle processes which constantly transform nitrogen among different forms, e.g., ammonium (NH4+), nitrite (NO2-), nitrate (NO3-), etc. Although studies have demonstrated the effects of environmental factors and microbial communities on the nitrogen cycle processes, yet, there are limited understandings of the coupling relationship and its underlying mechanism among the diverse nitrogen cycle processes driven by interaction between microbials and the environment. Such understanding will be critical for the global biogeochemical processes in general and the global nitrogen cycle in particular. .This proposed research project will be built upon our previous studies on identification of nitrogen sources, nitrogen deposition, water chemistry, and denitrification in the Jinshui River with a length of 87 km in the south aspect of the Qinling Mts (Shaanxi Province), China. Through systematic samplings, laboratory analyses, and data interpretation, our objectives are to reveal the temporal and spatial patterns of critical nitrogen cycle processes including nitrogen fixation, nitrification, denitrification, anaerobic ammonia oxidation (anammox), dissimilatory nitrate reduction to ammonium (DNRA) in river sediments along the longitudinal gradient in the riverine system, and consequently to determine the primary environmental factors which mediate nitrogen cycle processes. Afterwards, Metagenome/transcriptome sequencing, N15 isotope pairing technique，real-time quantitative PCR, and microcosm experiment will be employed to analyze the microbial community structure and its key enzyme-coding genes (nifH, amoA, nirK/nirS/nosZ; hzsA, nrfA) which regulate nitrogen cycle processes. Finally, we will explore the coupling mechanism among the critical microbial-driven nitrogen cycle processes and their association with the environmental factors. Our potential groundbreaking findings on such coupling mechanisms will provide guidelines for restoring biodiversity and improving ecosystem service in the riverine ecosystems.