Soil organic carbon and nitrogen dynamics following Spartina alterniflora invasion in a coastal wetland of eastern China

•Soil organic C stock increased with S. alterniflora invasion from 6 to 17 years.•Soil organic N stock unchanged with S. alterniflora invasion from 6 to 20 years.•S. alterniflora-derived C input was the highest in 17 years S. alterniflora soil.•SOM decomposition decreased with S. alterniflora invasion from 6 to 20 years.•Soil N cycling rate decreased with S. alterniflora invasion from 6 to 20 years.

Plant invasion has been reported to modify ecosystem carbon (C) and nitrogen (N) cycling processes and pools. The aims of this work were to identify the consequences of plant invasion on C and N dynamics in soil organic matter (SOM) and its fractions following invasion chronosequence. In this study, we investigated the soil C and N contents and the δ13C and δ15N values of the SOM, free light fraction (LF), intra-aggregate particulate organic matter (iPOM) and mineral-associated organic matter (mSOM) in invasive 6-, 10-, 17- and 20-year-old Spartina alterniflora communities and compared with bare flat land in a coastal wetland of eastern China. S. alterniflora invasion significantly increased soil organic carbon (SOC) and soil organic nitrogen (SON) contents in SOM fractions compared with the bare flat land. The SOC, iPOM-C and iPOM-N progressively increased, but the SON, mSOM-C and mSOM-N did not significantly change following S. alterniflora invasion chronosequence. The proportion of C in iPOM gradually increased, whereas that in mSOM decreased following S. alterniflora invasion chronosequence except for the 20-year-old S. alterniflora soil. The highest proportion of S. alterniflora-derived C in SOM and its fractions was found in 17-year-old soil covered by S. alterniflora. The decay rate of old C decreased and the mean residence time of C increased in SOM and its fractions following S. alterniflora invasion chronosequence. The δ15N values of soil under S. alterniflora were more enriched than were those in bare flat land, whereas the δ15N values depleted following invasion chronosequence. Our results show that S. alterniflora invasion significantly altered SOC dynamics following invasion chronosequence by changing C physical distribution in SOM, S. alterniflora-derived C input and C decomposition, ultimately having a greater impact on SOC incorporation relative to SON accumulation in a coastal wetland of eastern China.