Phosphorus availability as a primary constraint on methane emission from a freshwater wetland

► The effect of P enrichment on CH4 emission is unclear in wetlands. ► 4-year P addition decreased CH4 emissions in a temperate freshwater marsh. ► P addition's effect on CH4 emissions was time-dependent. ► P addition's effect on CH4 emissions did not vary with fertilization rates. ► Elevated P loading would suppress CH4 emissions in freshwater wetlands.