Impacts of Spartina alterniflora invasion on soil organic carbon and nitrogen pools sizes, stability, and turnover in a coastal salt marsh of eastern China

Plant invasion may impact ecosystem structure and function, and further affect soil organic matter (SOM) dynamics. However, the influence of plant invasion on soil organic carbon (C) and nitrogen (N) pools sizes, stability, and turnover in SOM of invaded ecosystems is not fully understood. In this study, soil C and N contents, and δ13C and δ15N values of free light fraction (LF), intra-aggregate particulate organic matter (iPOM) and mineral-associated organic matter (mSOM) were investigated in an invasive Spartina alterniflora community, adjacent bare flat and native Suaeda salsa and Phragmites australis communities. Short-term S. alterniflora invasion significantly enhanced organic C and N contents in SOM, free LF, iPOM, mSOM compared with bare flat and increased the proportion of allocated C in iPOM compared with S. salsa and P. australis soils (0–0.30 m depth). The proportion of the S. alterniflora-derived C in free LF and iPOM were significantly higher than that in mSOM, and the highest S. alterniflora-derived C content was found in iPOM of S. alterniflora soil. The most enriched δ15N values were found in S. alterniflora soil. Increased δ15N values and decreased C:N ratios from the free LF to iPOM to mSOM in S. alterniflora soil indicated a greater degree of decomposition. The results suggest that 10-year S. alterniflora invasion significantly alters soil organic C and N pools sizes and stability through changing plant residuals input, physical distribution of S. alterniflora-derived C and C turnover in SOM fractions.