1733 / 2019-08-28 12:15:11

Variation in taxonomic and functional profiles of bacterioplankton communities in response to changes in hydrologic regimes in the Three Gorges Reservoir

3、环境科学 > 专题6：湖泊-流域污染与生态

Natural freshwater aquatic systems have undergone extensive human disturbance especially with dam constructions. Such activities significantly alter the hydrological regime of rivers, which in turn affect the bacterioplankton community. Variation in community composition also leads to a shift in metabolic and ecosystem functions of the bacterioplankton. However, understanding on the underling mechanisms and the extent of the influence of the environment on the function and structuring of bacterioplankton communities remain unclear. In the present study, we used the Three Gorges Reservoir as the model system. High-throughput sequencing was used to investigated variations in community composition, and PICRUSt (phylogenetic investigation of communities by reconstruction of unobserved states) was applied to predict metabolic functions. Results showed that both taxonomic and predicted functional composition of communities significantly changed in response to the reservoir’s impoundment and subsequent shift of hydrological regimes. Actinobacteria dominated accompanied with increase in predicted functional categories of membrane transport and carbohydrate metabolism after impoundment. Moreover, comparisons at higher phylogenetic level or functional resolution showed more apparent variation after impoundment. For nitrogen metabolism, the bacterioplankton were mainly involved in dissimilatory NO3‒ reduction to NH4+ (DNRA), whereas nitrogen loss (NO3‒ to N2O or N2) through denitrification was relatively weaker. The DNRA process was enhanced while denitrification decreased after impoundment, as supported by the significant increase in nirB and nirD and the significant decrease of nosZ gene counts. The local-scale factors of environmental variables contributed the most to the variation of both the taxonomic and predicted functional compositions (29.7% and 33.1%), followed by hydrological (17.0% and 27.6%) and metrological (14.3% and 15.6%) factors. The contribution of hydrological variables alone was higher on functions than that of taxonomic profiles (20.1%% vs 4.5%). Generally, these results indicate that the shifts in hydrological regime had significant impacts on both the taxonomic and predicted functional composition of the bacterioplankton communities. Thus, dam construction and subsequent impoundment may alter the role of bacterioplankton in aquatic ecosystems.