The　purpose　of　this　study　was　to　assess　the　effects　of　wetland　plant　biochars　on　the　enzyme　activity　in　heavy　metal　contaminated　soil.　The　biochars　were　produced　from　Phragmites　australis　(PB),　Suaeda　salsa　(SB),　and　Tamarix　chinensis　(TB)　under　different　pyrolysis　temperatures　and　times.　The　detected　pyrolysis　products　showed　that　the　ash,　pH,　electrical　conductivity,　and　carbon　content　of　the　biochars　increased　significantly,　while　the　production　rate　of　the　biochars　decreased　with　increasing　pyrolysis　temperature　and　time.　The　results　of　the　adsorption　experiments　indicated　that　biochar　addition　could　effectively　reduce　the　concentration　of　Pb　and/or　Cd　in　the　Pb2+/Cd2+　single　or　mixed　solutions,　but　the　Pb2+　and　Cd2+　in　the　mixed　solution　indicated　a　competitive　adsorption.　A　30-day　incubation　experiment　was　conducted　using　salt　marsh　soil　amended　with　different　biochar　application　rates　to　investigate　the　short-term　effects　of　biochar　addition　on　Pb　and　Cd　immobilization.　The　PB　and　SB　significantly　immobilized　Pb　within　the　first　15 days,　but　Pb　remobilized　within　the　next　15-day　period.　In　contrast,　TB　addition　did　not　significantly　fix　Pb.　Moreover,　biochar　addition　promoted　the　conversion　of　Cd　from　the　residue　to　the　less　immobile　fractions.　The　addition　of　three　types　of　plant　biochar　had　no　significant　effect　on　the　urease　activity　in　wetland　soil　but　significantly　increased　soil　sucrase　activity.　PB　and　SB　significantly　promoted　catalase　activity,　while　TB　significantly　inhibited　soil　catalase　activity.　According　to　the　adsorption　effect,　the　fixation　effect,　and　the　promotion　of　enzyme　activities,　the　Suaeda　salsa　biochars　are　suitable　for　the　remediation　of　heavy　metal　pollution　in　wetland　soils.　©　2021,　The　Author(s),　under　exclusive　licence　to　Springer-Verlag　GmbH　Germany,　part　of　Springer　Nature.