Differential response of microbial diversity and abundance to hydrological residual time and age in cascade reservoirs

Purpose Freshwater sediments harbor taxonomically and metabolically diverse microbial communities, which play critical roles in aquatic ecosystems. However, little is known about the biogeographical patterns of assembly of such sedimentary communities, especially in cascade reservoirs of various age and hydrological characteristics. Methods Using Illumina sequencing and quantitative real-time polymerase chain reaction targeting the 16S rRNA gene, we investigated spatial patterns of both bacteria and archaeal communities across eight reservoirs (including Hongfeng Reservoir (HF y ), Hongjiadu Reservoir (HJD y ), Wujiangdu Reservoir (WJD s ), Dongfeng Reservoir (DF s ), Silin Reservoir (SL d ), Pengshui Reservoir (PS d ), Suofengying Reservoir (SFY d ), and Yinpan Reservoir (YP d )), forming the largest cascade reservoir system located on the Wujiang River, the tributary of the upper Yangtze River. Results Longer hydrological residual times promoted the proliferation of bacteria while reducing their diversity. In structures of different age, distinct archaeal communities were observed, with more abundant and diverse archaea in the earlier constructed reservoirs (HF y , WJD s ). Both environmental factors (redundancy analysis) and spatial scale (non-metric multidimensional scaling analysis) determined community structures. The abundances of bacteria and archaea were both positively correlated with the presence of nutrients. In particular, a shift in the composition of the sedimentary archaeal community was observed along with increasing trophic complexity of these reservoirs, from Thaumarchaeota- towards Euryarchaeota-dominated communities. Also, the preference of several phyla of bacteria, including Latescibacteria and Bacteroidetes, for anaerobic and eutrophic habitats was significantly positively correlated with the presence of nutrients in these reservoirs. Conclusion We demonstrated the existence of different distribution patterns of bacterial and archaeal communities in reservoir sediments, reflecting both deterministic and stochastic processes distinctly regulating the abundance of bacteria and archaea, in response to hydrological and biogeochemical changes after water impoundment in cascade reservoirs along a large river. Graphical abstract