It acts as a source of methanogenic substrate by releasing exudates and providing plant litter fall (Tong et al., 2012). Exotic Sonneratia forest and Spartina marsh both had much higher contents of TOC, TKN and TP than native wetlands, which could accelerate the production of CH4 in these systems. Secondly, plants with well-developed aerenchyma system provide a direct conduit for CH4to escape into the atmosphere without passing through the aerobic layer of surface soil and hence reduce the consumption of CH4 by methanotrophic bacteria (Biswas et al., 2007). The unique root structures of Sonneratia forest could be described as numerous chimneys emerging from the soil surface emitting CH4 produced by benthic microorganisms. Similarly,Tong et al. (2012)found that although more CH4 was oxidized in rhizospheres of Spartina than Cyperus marsh, soil–atmosphere flux of CH4 was significantly higher in Spartina marsh because of its higher production and more efficient transport of CH4 bySpartina than Cyperus marsh