The　mangrove　ecosystem　is　an　important　CO2　sink　with　an　extraordinarily　high　primary　productivity.　However,　it　is　vulnerable　to　the　impact　of　climate　warming　and　eutrophication.　While　there　has　been　extensive　research　on　plant　growth　and　greenhouse　gas　emission　in　mangrove　ecosystems,　microbial　communities,　the　primary　biogeochemical　cycling　drivers,　are　much　less　understood.　Here,　we　examined　whether　short-term　experimental　treatments:　(1)　eutrophication　with　a　supplement　of　185　g　N　m−2·year−1　(N),　(2)　3°C　warming　(W),　and　(3)　the　dual　treatment　of　N　and　W　(NW)　were　sufficient　to　alter　microbial　communities　in　the　sediment.　After　4　months　of　experiments,　most　environmental　factors　remained　unchanged.　However,　N　had　significant,　strong　effects　on　bacterial,　fungal,　and　functional　community　compositions,　while　the　effects　of　W　on　microbial　communities　were　weaker.　N　increased　bacterial　richness,　phylogenetic　diversity,　and　evenness,　owing　to　stronger　stochastic　processes　induced　by　eutrophication.　There　were　no　interactive　effects　of　N　and　W　on　bacterial,　fungal,　and　functional　community　compositions,　suggesting　that　joint　effects　of　N　and　W　were　additive.　Concomitant　with　higher　N2O　efflux　induced　by　N,　the　relative　abundances　of　most　bacterial　nitrogen　cycling　genes　were　increased　or　remained　changed　by　N.　In　contrast,　N　decreased　or　did　not　change　those　of　most　bacterial　carbon　degradation　genes,　while　W　increased　or　did　not　change　the　relative　abundances　of　most　of　bacterial　and　fungal　carbon　degradation　genes,　implying　higher　carbon　degradation　potentials.　As　the　most　abundant　inorganic　nitrogenous　species　in　mangrove　sediment,　ammonium　was　a　key　factor　in　shaping　microbial　functional　communities.　Collectively,　our　findings　showed　that　microbial　community　compositions　in　the　mangrove　sediment　were　highly　sensitive　to　short-term　N　and　W　treatments,　giving　rise　to　ecological　consequences　such　as　higher　N2O　efflux.　©　2022　Elsevier　B.V.