Research On The Relationship Between Bacterioplankton Community Composition And Environmental Factors In Heilongjiang Watershed

As an important component of freshwater ecosystem, bacterioplankton takes part in key biogeochemical reaction and plays crucial part in microbial loop in aquatic food web. Bacterioplankton community is highly changeable in freshwater ecosystem and responses to environmental pressure and disturbances complexly. Therefore, bacterioplankton community can be one of good indicators of water quality. As the methods evaluated bacterioplankton community composition developed, more and more studies focus on the determining factors that play key role in shaping bacterioplankton community composition. Dissolved organic matter in aquatic system is the greatest stocks in biosphere and is closely related to bacterioplankton community composition. Heilongjiang watershed is located in the extreme north of China. Dissolved organic matter that derived from dead plant and surface soil was carried into water by spring snowmelt, and it will influence the aquatic environment of Heilongjiang watershed. The aims of our study were to investigate the seasonal changes in bacterioplankton community composition of Heilongjiang watershed and the influences factors of bacterioplankton community composition in different season. In addition, our study also explored the influence of snowmelt on dissolved organic matter and bacterioplankton community composition of Heilongjiang watershed. The relationship between different bacterioplankton populations and different DOM components were also explored in our study.Water samples were collected at nine sits in the upstream midstream and downstream of Heilongjiang watershed in winter summer and autum season. Spring snowmelt occurred during sampling process. Denaturing gradient gel electrophoresis was adopted to investigate the bacterioplankton diversity and community composition of Heilongjiang watershed in different season. Differencing method of excitation-emission matrix fluorescence spectroscopy was employed to evaluate changes in dissolved organic matter of Heilongjiang watershed. Multivariate statistical analysis was applied to investigate the relationship between bacterioplankton community composition and environmental factors, dissolved organic matter and geographical factors.Results of denaturing gradient gel electrophoresis showed that the bacterioplankton diversity of Heilongjiang watershed was high in winter, summer and autum season and bacterioplankton community composition exhibited significant seasonal changes. The dominant populations of Heilongjiang watershed belonged to Alphaproteobacteria, Betaproteobacteria, Actinobacteria and Bacteroidetes by 16 S rDNA sequencing. Redundancy analysis demonstrated that NH4+-N, POC, components 2 and 4 were significant influence bacterioplankton community composition and T, p H, Chl-a, DOC, TP, NO2--N, components 1 and 3 also had effects on bacterioplankton community composition in winter season. While no significant correlation was found between environmental variables, DOM components and bacterioplankton community composition in summer season. The effects of snowmelt on changing dissolved organic matter and bacterioplankton community composition of Heilongjiang watershed. The relative content of components 2 and 3 decreased after snowmelt, while the relative content of component 4 increased. Mantel test indicated that bacterioplankton community composition was more closely related to environmental factors and dissolved organic matter than geographical factors. Variance partitioning showed that dissolved organic matter and environmental factors combined explained 51.70% of the total variation in Heilongjiang watershed bacterioplankton communities. The contribution of dissolved organic matter was larger than environmental factors. However, there was still 48.30% of variation that couldn’t be explained in our study. Distance-based redundancy analysis indicated that there was positive correlation between components 3 and the majority of populations, suggesting that component 3 could be degraded by bacterioplankton and was beneficial to the growth and metabolism of bacterioplankton. While, components 1, 2 and 4 had negative correlation with the majority of populations in Heilongjiang watershed, indicating that these components couldn’t be degraded by bacterioplankton.