富营养化湖泊微生物驱动的脱氮机制和生态效应

湖泊富营养化是全球性水环境问题，主要是氮磷过剩。我国湖泊众多，富营养化严重，磷负荷虽开始下降，氮负荷仍普遍高。近期发现厌氧氨氧化也是湖泊重要脱氮过程，但其脱氮比例因环境而异，调控机制不清楚。基于已有认识和前期基础，我们提出假说：在富营养化湖泊高负荷氮情境下，相对较高的磷促进藻类消长并形成颗粒微环境，有利于硝化反硝化和厌氧氨氧化协同脱氮。本项目结合湖泊采样、富集培养和生态模拟，利用高通量测序和氮同位素示踪，解析富营养化湖泊不同氮磷梯度下脱氮微生物功能菌群时空分布、脱氮过程及其与氮磷耦合的环境调控机制。进而从湖泊沉积物样品富集关键脱氮菌(群)，利用组学方法发掘湖泊微生物脱氮新类群和新通路，揭示其脱氮机制。并利用合成微生物生态学方法，构建针对湖泊的脱氮微生物功能菌群进行模拟脱氮，阐明其脱氮互作机制和生态效应。本项目能为认知湖泊微生物驱动的脱氮机制做出新贡献，也可为改善湖泊富营养化问题提供新依据。

Lake eutrophication, mainly with serious nitrogen and phosphorus contamination, has been a worldwide problem of the water environment. There are numerous lakes in China, but more than 70% of Chinese lakes are currently under different degree of eutrophication. Although there is a decline of phosphorus contamination in Chinese lakes since 2006, the nitrogen concentration is still at a relatively high level. Recent studies found that anammox is also an important nitrogen removal process in lakes, but its contribution to nitrogen removal ranged from 12% to 40% in different lake environments. The environmental regulation mechanism of anammox process in lakes is unclear. We hypothesized that in eutrophic lakes with relatively high concentration of nitrogen, a relatively higher level of phosphorus will increase collaborative nitrogen removal by denitrification and anammox. As higher phosphorus enhances the growth of algal cells, which will result in an enrichment of algal particles at the surface of sediments. The massive accumulation of died algal cells provides proper conditions for denitrification and anammox, thus increase the nitrogen removal. This project will use experiments at scales of lake sampling, enrichment systems and simulated bio-reactors to reveal the microbial driving mechanism of nitrogen removal in eutrophic lakes. Two representative eutrophic shallow lakes (i.e., Taihu Lake and Lake Donghu) will be selected to represent the small and large lakes, respectively. Samples will be collected from sites with a gradient of nitrogen and phosphorus contamination in different seasons. First, different functional groups will be investigated by high-throughput sequencing of functional genes (e.g., narG, nirS/K, norB, nosZ, hzsA, hzo) and metagenomes. The distribution and succession of microbes related to nitrogen removal processes and their environmental regulations will be clarified. Second, the core bacteria that involving in nitrogen removal of eutrophic lakes will be enriched. In combination of isotope tracer analysis and microbiome-related methods, some novel microbial groups and new pathways involving in nitrogen removal in eutrophic lakes will be excavated, and their driving mechanisms for nitrogen removal will be elucidated through microbial -omics techniques. Finally, with the help of the synthetic microbial ecological theories and methods, synthetic functional microbial community that with high potential of nitrogen removal for eutrophic lakes will be assembled. The synthetic functional microbial community will be further used to test their interactions in nitrogen removal with simulated bio-reactors. This proposal gives novel contribution to understand microbial driving mechanism of nitrogen removal in eutrophic lakes, and further provides new evidence to improve the worldwide problem of lake eutrophication.