Coastal　wetlands　face　unprecedented　challenges　from　sea-level　rise;　however,　the　effects　of　increased　waterlogging　and　salinity　on　soil　respiration　remain　unclear,　particularly　given　the　contrasting　stress　tolerance　strategies　of　dominant　marsh　species　such　as　native　Phragmites　australis　and　invasive　Spartina　alterniflora.　We　conducted　a　mesocosm　experiment　to　compare　soil　respiration　responses　to　waterlogging　(control:　low　water　level;　treatment:　high　water　level)　and　salinity　(control:　0　ppt;　treatments:　5,　15,　and　30　ppt)　between　these　two　species,　while　also　examining　the　underlying　mechanisms　and　the　role　of　drainage.　Under　waterlogged　conditions,　high　water　levels　significantly　suppressed　soil　respiration,　with　P.　australis　exhibiting　a　greater　reduction　than　S.　alterniflora　(78.9　%　vs.　74.4　%).　The　species　showed　distinct　responses　to　salinity:　high　salinity　(30　ppt)　caused　a　more　pronounced　reduction　in　P.　australis　than　in　S.　alterniflora　(56.4　%　vs.　28.9　%).　Drainage　conditions　fundamentally　altered　these　responses;　P.　australis　showed　a　greater　post-drainage　enhancement　under　high　water　level　(42.4　%　vs.　12.9　%)　but　consistently　exhibited　higher　sensitivity　to　salinity.　These　species-specific　responses　were　mediated　by　differential　changes　in　root　biomass,　microbial　biomass　carbon,　and　carbon-cycling　enzyme　activities.　Principal　component　analysis　revealed　clear　ecological　niche　separation　along　the　stress　gradients,　with　S.　alterniflora　maintaining　higher　biological　activity　and　P.　australis　displaying　greater　stress　sensitivity　under　severe　combined　conditions.　The　combined　effects　of　waterlogging　and　salinity　revealed　non-additive　impacts　on　soil　respiration,　with　S.　alterniflora　demonstrating　superior　tolerance　through　sustained　microbial　activity　and　root　functioning.　Our　findings　underscore　the　importance　of　considering　species-specific　adaptive　strategies　and　tidal　dynamics　when　predicting　coastal　wetland　carbon　cycling　under　future　sea-level　rise　scenarios,　as　the　differential　stress　responses　of　these　ecologically　significant　species　may　substantially　influence　ecosystem　carbon　dynamics.