LAUSR

Abstract The water column (fluidic) and sediments (non-fluidic) represent two distinct habitats in lakes. Planktonic and sedimentary bacterial communities are fundamental components of the biogeochemical processes within freshwater lakes. Anthropogenic activities induced eutrophication has been recognized as one of the most severe environmental problems for the lake ecosystem. However, little is known regarding the responses of bacterial communities in fluidic and non-fluidic lake habitats to eutrophication nor the underlying ecological mechanisms. Here, we investigated the planktonic and sedimentary bacterial communities from a series of freshwater lakes across a range of trophic states. We observed a high heterogeneity in bacterial community composition between habitats and along the trophic gradient. Alpha diversity of the sedimentary bacterial community decreased monotonically with increased eutrophication, whereas that of planktonic bacterial community exhibited a downward arched (parabolic) pattern along the trophic gradient. Co-occurrence network analysis revealed that the network of planktonic bacterial community is more susceptible to eutrophication than the network of sedimentary bacterial community. Null-model analysis suggested that eutrophication enhanced the contributions of stochastic processes in controlling the assembly of planktonic and sedimentary bacterial communities. However, the importance of stochastic processes in the assembly of planktonic bacterial community reduced within lakes experiencing extreme eutrophication. The differences in environmental characteristics and community assembly processes between water and sediment may account for the discrepancy in bacterial diversity patterns of the two lacustrine habitat types along the same trophic gradient. These results offer insights into the successional patterns of bacterial communities in freshwater lakes subjected to anthropogenic eutrophication. Moreover, the different distribution patterns and assembly processes of bacterial communities act as indicators of specific habitat responding to environmental gradients.