Seasonal variation in CH4 emission and its C-13-isotopic signature from Spartina alterniflora and Scirpus mariqueter soils in an estuarine wetland

Although invasions by non-native species represent a major threat to biodiversity and ecosystem functioning, little attention has been paid to the potential impacts of these invasions on methane (CH4) emission and its C-13-CH4-isotope signature in salt marshes. An invasive perennial C-4 grass Spartina alterniflora has spread rapidly along the east coast of China since its introduction from North America in 1979. Since its intentional introduction to the Jiuduansha Island in the Yangtze River estuary in 1997, S. alterniflora monocultures have become the dominant component of the Jiuduansha's vegetation, where monocultures of the native plant Scirpus mariqueter (a C-3 grass) used to dominate the vegetation for more than 30 years. We investigated seasonal variation in soil CH4 emission and its C-13-CH4-isotope signature from S. alterniflora and S. mariqueter marshes. The results obtained here show that S. alterniflora invasion increased soil CH4 emissions compared to native S. mariqueter, possibly resulting from great belowground biomass of S. alterniflora, which might have affected soil microenvironments and /or CH4 production pathways. CH4 emissions from soils in both marshes followed similar seasonal patterns in CH4 emissions that increased significantly from April to August and then decreased from August to October. CH4 emissions were positively correlated with soil temperature, but negatively correlated with soil moisture for both S. alterniflora and S. mariqueter soils (p 0.05). Generally, the CH4 emissions from both invasive S. alterniflora and native S. mariqueter soils in the salt marshes of Jiuduansha Island were very low (0.01-0.26 mg m(-2) h(-1)), suggesting that S. alterniflora invasion along the east coast of China may not be a significant potential source of atmospheric CH4.National Basic Research Program of China [2006CB403305]; National Science Foundation of China [30670330]; Ministry of Education of China [20050246013