Microbial necromass carbon contributed to soil organic carbon accumulation and stabilization in the newly formed inland wetlands.

Inland wetlands might be an important "carbon sink", and the chronosequence development of newly formed inland wetlands offers a natural and suitable opportunity for studying the dynamic effect of plant and microbial necromass carbon (PlantC and MNC) on the soil organic carbon (SOC) stabilization. The space-for-time chronosequence approach was used and plots were established in the three ages of newly formed inland wetlands (2, 5, and 16 years). Soil samples were collected in the surface (0-10 cm) and subsurface soil (20-30 cm). Results showed that accumulation of SOC, PlantC, and MNC were significantly larger in the surface than those in the subsurface soil. Moreover, MNC stocks were more abundant than PlantC in the wetland ecosystem both in the surface and subsurface soil. During the chronosequence development, dynamics of SOC and its components accumulation were similar to MNC, both exhibiting an increasing and then decreasing trend in the surface and subsurface soil, except for free particulate organic carbon in the subsurface soil. Structural equation models revealed that changes of MNC affected by environmental variables were the main cause of MAOC dynamics both in the surface and subsurface soil, suggesting that contribution of MNC to MAOC would be the key way of carbon stabilization in the newly formed inland wetlands. Furthermore, MNC accumulation in the surface soil was closely linked to pH, CEC, and soil texture, while in the subsurface soil affected by soil nutrients (TN and NH-N). Particularly, despite the decreasing SOC stocks in the 16-year wetland, the stability has significantly enhanced due to the increasing persistent individual amino sugars. This study provides new information on the dynamics of SOC accumulation and highlights the significance of MNC on the SOC sequestration in the newly formed inland wetlands, which is important for the understanding of wetland SOC stock dynamics and stabilization mechanisms.