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Uncoveringwhich environmental factors have the greatest influence on community diversity patternsand how ecological processes govern community turnover are key questions related to understanding community assembly mechanisms.However,the mechanisms regulating diversity patterns of aquatic bacterial communities in lake ecosystems remainspoorly understood.Here we present nearly a decade-long study of bacterioplankton communities from the eutrophic Lake Donghu(Wuhan,China)using 16S rRNA gene amplicon sequencing.We found strong repeatable seasonal patterns for the overall community,common(detected in more than 50%samples)or dominant bacterial taxa(relative abundance > 1%).Moreover,communitycomposition tracked the seasonaltemperature gradient,indicating that temperature is an important environmental factorcontrolling observed diversity patterns.Total phosphorus also contributed significantly to the seasonal shifts in bacterioplankton composition.However,any spatial pattern across the main lake areas wasoverwhelmed by temporal variability of bacterioplankton communities.Phylogenetic analysis further indicated that 75%-82%of community turnover was governed by homogeneous selection due to consistent environmental conditions within seasons,suggesting that the microbial communities in Lake Donghuare mainly controlled by niche-based processes.Therefore,dominant niches available within seasons might be occupied by similar combinations of bacterial taxa with modest dispersal rates throughout different lake areas.