三峡库区水体中固氮微生物多样性及其影响因素

Nitrogen-fixing microbial diversity and its influencing environmental variables in waters Three Gorges Reservoir

【目的】研究分析不同时空条件下三峡库区水体固氮微生物多样性,并探讨其与地球化学参数的相关性。【方法】采集三峡库区不同时间(三月份和六月份)和空间(干流与支流)的水体样品,对其进行地球化学参数分析,并通过构建克隆文库分析样品中固氮功能基因(nifH)的多样性进而探讨其与水体地化参数的相关关系。【结果】统计分析显示三峡库区水体固氮微生物α-多样性和群落组成具有时空差异。支流水体样品的固氮微生物α-多样性高于干流水体样品;六月水体样品的固氮微生物α-多样性高于三月水体样品。三峡库区三月水体样品中的固氮微生物群落以Proteobacteria (50.3%)和Firmicutes (40.0%)为主;六月水体样品的固氮微生物群落以Proteobacteria(48.4%)、Firmicutes(25.4%)和Cyanobacteria(19.0%)为主。Mantel检验结果显示:固氮微生物群落结构的差异与温度、pH和DIC等地球化学参数具有显著(P<0.05)相关性,其中温度和pH的相关性系数最大。【结论】三峡库区固氮微生物的种群结构和多样性具有时空差异,影响三峡水库水体中固氮微生物群落结构与多样性的主要环境因素为温度和pH,同时浊度、DIC、氨氮也对库区水体固氮微生物群落结构和多样性有一定的影响。

[Objective] To explore the diversity of nitrogen-fixing microbial community and its response to geochemical parameters in the water of the mainstream and branches in the Three Gorges Reservoir (TGR)[Methods] A total of 18 water samples were collected from the mainstream and branches of the TGR before and after drainage (in March and June). The physical and chemical parameters of the samples were measured, and nifH gene diversity was analyized by using clone library-based phylogenetic analysis. The geochemical parameters of water bodies were correlated with the diversity and community composition of nitrogen-fixing microbial.[Results] The geochemical parameters differed significantly before (in March) and after (in June) drainage. The nitrogen-fixing microbes were dominated by Proteobacteria (50.3%) and Firmicutes (40.0%) the TGR waters in March (before drainage), in contrast with the dominance of Proteobacteria (48.4%), Firmicutes (25.4%) and Cyanobacteria (19.0%) in June (after drainage). Significant temporal and spatial variations were observed among the nitrogen-fixing microbial community composition and diversity as indicated by statistical analysis (Cluster and CCA analyses). The diversity of nitrogen-fixing microbes in the TGR waters after drainage (in June) was higher than before. The diversity of nitrogen-fixing microbes was higher in waters from tributaries than that from the main stream. Mantel test showed that the composition of nitrogen-fixing microbes was significantly correlated with the geochemical parameters of water. Water temperature was the most important factor affecting the community and variety of nitrogen-fixing microbes in the TGR waters.[Conclusion] The nitrogen-fixing microbial community compositions in the TGR waters show significant temporal and spatial variations, which could be ascribed to the different geochemical parameters, especially water temperature.