Species-Specific Impacts of Invasive Plant Success on Vertical Profiles of Soil Carbon Accumulation and Nutrient Retention in the Minjiang River Tidal Estuarine Wetlands of China

The increasing presence of successful invasive plant species can have an impact on wetlands capacity to store and release C. We have investigated the relationships between stocks of different soil organic carbon (SOC) along the soil vertical profile and invasive plant success in a China wetland. In stands dominated by the exotic invasive species Spartina alterniflora and the native invasive Phragmites australis soil organic-carbon concentrations (SOC) were higher (12% and 9%, respectively) than in plots of a native species, Cyperus malaccensis, whereas SOC content (g m−2) was 18% and 17% lower under P. australis than under S. alterniffolia and C. malaccensis, respectively. Soils under both invasive species had the concentrations and contents of light-fraction organic carbon (LFOC), light-fraction organic nitrogen (LFON) at 30–60 cm of soil depth and labile organic carbon (LOC) concentrations at 0–10 cm higher than soils under native species. The invasive species had higher total aboveground, total biomasses and lower shoot:root ratios than the native species. The success of both invasive species was associated with higher growth rates and accumulation of nutrients in biomass than in the native species and also accumulation of C in plant soil system. The stands currently dominated by the invasive species were recently occupied by monospecific stands of the native C. malaccensis, strongly suggesting that all or most of the current soil differences were due to the invasions. Higher sand fraction in C. malaccensis community and higher clay fraction in P. australis community relative to the native species, were correlated with higher soil N and P concentrations in invaded stands. The results suggest that different vegetation cover with distinct shoot/root ratio can change soil structure by favoring sedimentation of different particle size classes. Thus, despite both invasive species have some common traits, the results also showed that different invasive species with partially distinct impacts on soil and nutrient uses can succeed under the same conditions. The traits conferring invasive success are thus not necessarily species-specific. A clear change in the general accumulation of C, N and P in the plant-soil system was related to the invasive plant success in this wetland areas