To　understand　the　dynamics　of　planktonic　microbial　community　and　its　metabolism　processes　in　subtropical　drinking　water　river-reservoir　system　with　lower　man-made　pollution　loading,　this　study　selected　Dongzhen　river-reservoir　system　in　Mulan　Creek　as　object　to　investigate　spatial-temporal　characteristics　of　community　profile　and　functional　genes　involved　in　biological　metabolism,　and　to　analyze　the　influence　of　environmental　factors.　The　results　indicated　that　Proteobacteria　and　Actinobacteria　were　the　most　diverse　phyla　with　proportion　ranges　of　9%–80%　in　target　system,　and　carbohydrate　metabolism　(5.76-7.12　×　10−2),　amino　acid　metabolism　(5.78-7.21　×　10−2)　and　energy　metabolism　(4.07-5.17　×　10−2)　were　found　to　be　the　dominant　pathways　of　biological　metabolism.　Although　there　were　variations　in　biological　properties　both　spatially　and　temporally,　seasonal　variation　had　a　greater　influence　on　microbial　community　and　biological　metabolism,　than　locational　differences.　Regarding　the　role　of　environmental　factors,　this　study　revealed　that　microbial　diversity　could　be　affected　by　multiple　abiotic　factors,　with　total　organic　carbon,　total　phosphorus　and　temperature　being　more　influential　(absolute　value　of　standardized　regression　weights　＞2.13).　Stochastic　processes　dominated　the　microbial　community　assembly　(R2　of　neutral　community　model　=　0.645),　while　niche-based　processes　differences　represented　by　nutrients,　temperature　and　pH　level　played　secondary　roles　(R　＞　0.388,　P　©　2023　Elsevier　Inc.