Consequences of short-term C4 plant Spartina alterniflora invasions for soil organic carbon dynamics in a coastal wetland of Eastern China

The impacts of plant invasions are of great concern in the terrestrial carbon (C) cycling. However, the consequences of plant invasions for soil organic carbon (SOC) dynamics are not well understood. In this study, we conducted a field experiment to examine the effects of an exotic C4 perennial grass, Spartina alterniflora, on SOC pool and its fractions by comparing with native C3 plant Suaeda salsa and Phragmites australis soils and bare flat in a coastal wetland of Eastern China for one year. Soil samples from S. alterniflora invaded soil, bare flat, S. salsa and P. australis soils were measured for the soil water-soluble organic carbon (WSOC), microbial biomass carbon (MBC), cumulative CO2-C mineralization (MINC), soil organic carbon (SOC), total nitrogen (TN) and the C:N ratio. Short-term S. alterniflora invasions significantly increased WSOC, MBC, MINC, SOC and TN levels in the upper 0–30 cm soil layer compared to bare flat and native C3 plant communities, but significantly decreased WSOC/SOC, MBC/SOC and MINC/SOC ratios relative to bare flat. S. alterniflora invasions also considerably increased aboveground and root biomass. The C:N ratio in S. alterniflora soil was significantly higher than that in S. salsa and P. australis soils, but with no difference from bare flat. Our results suggest that S. alterniflora invasions could enhance SOC sequestration possibly due to large amounts of litter biomass input but lower proportion of soil labile organic carbon pool fractions and mineralizable carbon in per unit SOC. Plant invasions could change the quantity and quality of the SOC pool and thus, have potential impacts on ecosystem functioning and global C cycling.