Impacts of Spartina alterniflora invasion on soil inorganic carbon in coastal wetlands in China

Biological invasion has profoundly influenced coastal soil reservoirs of carbon. Previous carbon studies regarding biological invasion in coastal wetlands mainly focused on soil organic carbon; however, little is known about the mechanisms that control soil inorganic carbon (SIC, e.g., carbonates) variation. In order to explore our understanding, we used structural equation modeling (SEM) to evaluate controlling mechanisms of SIC in response to Spartina alterniflora (Loisel) invasion in the east-central China coast, where there is a lack of native salt marsh species. A space-for-time substitution method was used to identify sampling sites, assuming it has the capability to quantify the soil-vegetation relationship along a gradient of the increasing S. alterniflora age (17 year). The results showed that soil inorganic carbon density (SICD) at the 0.3-0.6 m depth exhibited a decline under S. alterniflora invasion, while there was no substantial change at the depths of 0-0.3 m and 0.6-1 m. The majority of the variances in SICD changes could be explained by S. alterniflora invasion and key soil physicochemical variables. In SEM, S. alterniflora invasion, soil water content, and soil texture presented direct influence on SICD throughout the soil profile (i.e., to 1 m depth). Soil salinity presented direct influence on SICD in the upper 0.6 m soil, while pH played an important role in the depth of 0.6-1 m. These results highlight that dynamics of SIC processes are probably controlled by interactions among S. alterniflora invasion and key soil physicochemical variables.