“Plastisphere”,　microbial　communities　colonizing　plastic　debris,　has　sparked　global　concern　for　marine　ecosystems.　Microbiome　inhabiting　this　novel　human-made　niche　has　been　increasingly　characterized;　however,　whether　the　plastisphere　holds　crucial　roles　in　biogeochemical　cycling　remains　largely　unknown.　Here　we　evaluate　the　potential　of　plastisphere　in　biotic　and　abiotic　denitrification　and　nitrous　oxide　(N2O)　production　in　estuaries.　Biofilm　formation　provides　anoxic　conditions　favoring　denitrifiers.　Comparing　with　surrounding　bulk　water,　plastisphere　exhibits　a　higher　denitrifying　activity　and　N2O　production,　suggesting　an　overlooked　N2O　source.　Regardless　of　plastisphere　and　bulk　water,　bacterial　and　fungal　denitrifications　are　the　main　regulators　for　N2O　production　instead　of　chemodenitrification.　However,　the　contributions　of　bacteria　and　fungi　in　the　plastisphere　are　different　from　those　in　bulk　water,　indicating　a　distinct　N2O　production　pattern　in　the　plastisphere.　These　findings　pinpoint　plastisphere　as　a　N2O　source,　and　provide　insights　into　roles　of　the　new　biotope　in　biogeochemical　cycling　in　the　Anthropocene.　©　2022,　The　Author(s).