Conditionally　rare　bacteria　are　ubiquitous　and　perhaps　the　most　diverse　of　microbial　lifeforms,　but　their　temporal　dynamics　remain　largely　unknown.　High-throughput　and　deep　sequencing　of　the　16S　rRNA　gene　has　allowed　us　to　identify　and　compare　the　conditionally　rare　taxa　with　other　bacterioplankton　subcommunities.　In　this　study,　we　examined　the　effect　of　season,　water　depth,　and　ecological　processes　on　the　fluctuations　of　bacterial　subcommunities　(including　abundant,　conditionally　rare,　moderate,　and　rare　taxa)　from　three　subtropical　reservoirs　in　China.　We　discovered　that　the　conditionally　rare　taxa　(CRT)　made　up　49.7　to　71.8%　of　the　bacterioplankton　community　richness,　and　they　accounted　for　70.6　to　84.4%　of　the　temporal　changes　in　the　community　composition.　Beta-diversity　analysis　revealed　strong　seasonal　succession　patterns　among　all　bacterioplankton　subcommunities,　suggesting　abundant,　conditionally　rare,　moderate,　and　rare　taxa　subcommunities　have　comparable　environmental　sensitivity.　The　dominant　phyla　of　CRT　were　Proteobacteria,　Actinobacteria,　and　Bacteroidetes,　whose　variations　were　strongly　correlated　with　environmental　variables.　Both　deterministic　and　stochastic　processes　showed　strong　effect　on　bacterioplankton　community　assembly,　with　deterministic　patterns　more　pronounced　for　CRT　subcommunity.　The　difference　in　bacterial　community　composition　was　strongly　linked　with　seasonal　change　rather　than　water　depth.　The　seasonal　patterns　of　CRT　expand　our　understanding　of　underlying　mechanisms　for　bacterial　community　structure　and　composition.　This　implies　their　importance　in　the　function　and　stability　of　freshwater　ecosystem　after　environmental　disturbance.　©　2019,　Springer　Science+Business　Media,　LLC,　part　of　Springer　Nature.