Labile and Recalcitrant Soil Carbon and Nitrogen Pools in Tidal Salt Marshes of the Eastern Chinese Coast as Affected by Short-Term C4 Plant Spartina alterniflora Invasion

Terrestrial ecosystems carbon (C) and nitrogen (N) cycles, affected by plant invasion, are not fully understood. In this study, the impact of 10 years Spartina alterniflora invasion on soil organic matter (SOM), labile, and recalcitrant pools was examined comparing with bare flat and native Suaeda salsa and Phragmites australis communities in tidal salt marshes of the Eastern Chinese coast. Short-term S. alterniflora invasion significantly raised C and N concentrations in SOM, labile and recalcitrant pools compared to bare flat, S. salsa and P. australis soils. Spartina alterniflora soil had higher recalcitrant index for C relative to bare flat. The proportion of S. alterniflora-derived C and the decomposition rate of old C in the labile pool were significantly higher than those in the recalcitrant pool. However, the S. alterniflora-derived C stock of the recalcitrant pool was much greater than that of the labile pool. The SOM and recalcitrant pools in S. alterniflora soil had significantly higher delta N-15 levels compared with bare flat, indicating an increased N loss following S. alterniflora invasion. The results suggested that short- term S. alterniflora invasion significantly enlarged soil organic C and N pools via altering SOM input and decomposition.