Contribution of invasive species Spartina alterniflora to soil organic carbon pool in coastal wetland: Stable isotope approach

Abstract

Aims Spartina alterniflora was introduced into China because of its strong sedimentation promotion ability, currently, it became one of the most invasive species along coastal areas. Most researches focused on its high productivity which directly increased soil carbon(C) input. However, little is known about its indirect contribution to soil carbon via increased sedimentation. Methods Spartina alterniflora patches with different invasion history(4, 6, and 10 years) was selected in Chongming Dongtan wetland, and Phragmites australis and mudflat were chosen as control respectively. The plant, soil and water samples were collected for C and nitrogen(N) analysis. Based on the stable isotope ratio of C and N in plant and soil organic carbon, the contribution of soil organic carbon pool from S. alterniflora patches were estimated by using 2 and 3 sources mixing model, respectively. Important findings(1) The soil organic C content and stable carbon isotope ratio of S. alterniflora patches increased with time. Spartina alterniflora invasion cumulatively enhanced soil organic carbon pool. The soil C:N ratio decreased with invasion history and became close to the redfield ratio, indicating the important role of sedimentation input.(2) The contribution of invasive S. alterniflora to soil organic carbon pool increased with time, but the sedimentation contribution dropped gradually. In patch with 4 years invasion history, the contribution ratio of sedimentation was more than 90.0%. While in patch invaded 10 years ago, the sedimentation contributionreduced by 18.4%, and in comparison, S. alterniflora contributed up to 73.5% to soil organic carbon pool. These findings suggested that S. alterniflora contributed to soil organic carbon pool mainly by promoting sedimentation in early invasion period, while gradually relied on its own productivity with invasion time. Key words contribution ratio, mixing model, Spartina alterniflora, soil carbon pool, stable isotope