Abstract: Spartina alterniflora has rapidly and extensively encroached on China’s coastline over the past decades. Among the coastal areas invaded by S. alterniflora, over 93% are mudflats. However, the effect of S. alterniflora invasion on soil organic carbon (SOC) stocks of coastal mudflats has not been systematically studied on a national scale. Here, we quantified nationwide changes in SOC stocks in coastal mudflats associated with S. alterniflora invasion between 1990 and 2015 and predicted future changes in S. alterniflora SOC stocks under different emission scenarios by 2100. We found that S. alterniflora invasion significantly enhanced SOC stocks in coastal China. The total S. alterniflora SOC stocks increased considerably from 0.43 Tg C in 1990 to 3.2 Tg C in 2015. Nonetheless, the benefit of S. alterniflora invasion of coastal SOC stock may be weakened by continuing climate change. Future predictions suggest that S. alterniflora SOC stock may steadily increase to 5.1 Tg C by 2040s but decrease afterward – most rapidly under the high emission scenario. These findings overturned the traditionally thought that S. alterniflora invasion would reduce ecosystem services by highlighting that the historical invasion of S. alterniflora has broadly and consistently enhanced blue carbon stock in coastal ecosystems.
