温室效应对水层过量氮转化的影响及漂浮植物的调节机制

温室效应与水体氮循环之间关系密切，以往研究多关注于N2O等温室气体排放对温室效应的贡献，忽视了温室效应对水体过量氮转化的影响。本申请拟采用13CO2及N-15双标记及稳定同位素质谱分析技术，结合稳定性同位素核酸探针技术等分子生物学手段，研究在温室效应的大气CO2浓度增高、增温条件下，富营养化水体不同深度水层参与氮生物转化的功能菌群多样性、结构，以及氮生物转化关键过程的变化。同时，借助收集不同水层释放生物脱氮气态产物的新方法，评价CO2浓度增高、增温对水体排放15N2O、15N2O/15N2的影响。在此基础上，研究漂浮水生植物对大气CO2浓度、水体CO2-碳酸盐系统平衡、有机碳量、热力学及理化环境因子分层效应及氮转化功能菌群的影响，分析漂浮植物通过调节上述因素对CO2浓度增高、增温及水体排放N2O的调节作用。通过研究，期望为温室效应对水体过量氮转化的影响及漂浮植物的调节作用机制提供理论基础。

There are strong interactions between greenhouse effect and nitrogen cycle in ecosystem. However, most of the previous studies have focused on the contribution of N2O emission from aquatic ecosystem to greenhouse effect, whereas the effect of greenhouse effect on nitrogen cycle in aquatic ecosystem has been receiving little attention. In this proposed research, double 13CO2 and 15N labelling technology followed with Isotope-ratio mass spectrometry analysis, in combination with stable isotope probing technique, will be used to study the effect of increasing atmospheric CO2 levels and temperature on the diversity, composition and function of nitrogen cycling bacteria and transformation of nitrogen in different depths of eutrophic water. A new gas collecting method to collect in-situ the release of nitrogen gas from different layers of waters will be used to measure the effect of increasing atmospheric CO2 levels and temperature on 15N2O emission and 15N2O/15N2. Base on above studies, the effect of floating aquatic macrophytes on atmospheric CO2 levels, water temperature, CO2-carbonates balance in water, organic carbon, thermal stratification, physical and chemical properties under thermal stratification and functional nitrogen cycling bacteria will be studied to help to clarify the mechanisms involved in how floating aquatic macrophytes mediate the increasing atmospheric CO2 levels and temperature and N2O emission from water. Through the proposed research, it is expected to provide the theory base for how greenhouse effect influence the excessive nitrogen transformation in water and how floating aquatic macrophytes mediate these processes.