Effects of Spartina alterniflora invasion and subsequent mangrove restoration on soil nitrogen mineralization in Quangang, China

The Spartina alterniflora has severely invaded the coastal mangrove ecosystems in China. Here, we attempt to evaluate the invasion effect of S. alterniflora and the restoration effect of mangrove wetlands from the perspective of the nitrogen cycle characteristics. The inorganic nitrogen content, soil nitrogen mineralization, ammonification, and nitrification rate of uninvaded mudflats with those of invaded S. alterniflora site and native Kandelia obovata site at different restoration stages were compared. The results showed that the NH4+-N was the dominant form of soil inorganic nitrogen at all sites. Owing to its higher ammonification rates, the nitrogen mineralization rates at S. alterniflora site were highest in spring and summer among all sites except for mudflat. The young mangrove (1 year and 8 years) had significantly higher soil inorganic nitrogen content but lower nitrogen mineralization than the mature mangrove, indicated the short-term response to restoration. The S. alterniflora invasion did not enhance soil nitrogen mineralization comparing with preinvaded mudflat, but it used more NH4+-N relative to K. obovata due to its higher soil nitrogen mineralization than mangrove communities in germination and growing seasons.