Abstract: Natural wetland is one of the key sources for atmospheric methane. Spartina alterniflora invasion generally increases the soil organic carbon content in coastal marshes of China. In this study, three intact soil cores were collected from the coastal brackish marshes having been invaded by S. alterniflora for 8, 11 and 15 years, respectively, and a pot experiment was conducted to investigate the effects of soil organic carbon content on the methane emission from coastal brackish marsh. The soil organic carbon content increased with the increasing year of S. alterniflora invasion, and the methane emission had an apparent seasonal pattern, with the peak in September. During growth season, the mean methane flux of the marsh having been invaded by S. alterniflora for 15 years and with the soil organic carbon content of 12.97 g·kg^-1 amounted to 2.94 mg·m^-2·h^-1, which was significantly higher than that (1.95 and 2.34 mg·m^-2·h^-1) of the marshes after 8 and 11 years S. alterniflora invasion and with the soil organic carbon content of 8.11 and 9.16 g·kg^-1, respectively. It was considered that the increased soil organic carbon content not only increased the supply of dissolved organic carbon for methanogens, but also- stimulated the growth of methanogens, which together elevated the methane emission from the coastal marshes invaded by S. alterniflora.

Key words: the northwest of Shanxi Province, land use, change dynamics, driving force.