The soils under these four vegetations types were all a net source of greenhouse gases throughout the year, while alien Sonneratia forest and Spartina marsh had significantly higher greenhouse gas emission than their respective native counterparts Kandelia and Cyperus (Fig. 4), which supports our first hypothesis. Besides, soil organic carbon stock was also found significantly higher in the two alien vegetations although they were relatively young as opposed to native vegetations which accords well with our second hypothesis