Effects of exotic Spartina alterniflora on vertical soil organic carbon distribution and storage amount in coastal salt marshes in Jiangsu, China

•S. alterniflora increases the vertical soil organic carbon (SOC) distribution depth in local salt marshes.•Total soil organic carbon storage (SOCS) of 0-300 cm depth in the Jiangsu salt marsh is 84.90 × 1010 g.•The deep soil (100-300 cm) SOC accounts more than 50% of 0-300 cm SOC in the Jiangsu salt marshes.

Coastal wetlands soil organic carbon (SOC) plays an important role in global carbon sequestration, and exotic S. alterniflora affects the coastal ecosystem's functions including SOC storage (SOCS). We investigated the vertical deep soil SOC distribution (0-300 cm) in Jiangsu salt marsh and estimated its changes. The results show that (1) exotic S. alterniflora increases the SOC, with higher densities (g kg−1) in both topsoil and deep soil in its colonized area, and subsequently increases the SOCS vertical depth (cm) distribution. Such influences become more prominent with time since the introduction of S. alterniflora. The deepest SOC distribution (180 cm) and the highest SOC content (2.14 ± 0.19 g kg−1) in the deep layer (50-300 cm) were found in the zones where S. salsa - S. alterniflora co-exist (SSI). The vertical SOC distribution in zones where multi-species co-exists is deeper than that in mono-species dominated zones; (2) The deep soil (100-300 cm) SOC accounts more than 50% of 0-300 cm SOC in Jiangsu salt marsh, suggesting that SOC content of deep soil should not be ignored when calculating the global soil carbon stock; (3) Total SOCS within 0-300 cm in Jiangsu salt marshes (107.84 × 106 m2) is 84.90 × 1010 g, of which 0-100 cm, 100-200 cm and 200-300 cm layer accounts for 38.25%, 30.72% and 31.03%, respectively. The size of the SOCS (0-300 cm) in the Jiangsu salt marshes relatively to the global biome (0.36 × 10−6) is in a lower proportion of the range of salt marsh area to global biome area (0.89 × 10−6). The S. alterniflora salt marsh contributes most of the SOCS in the 0-300 cm and 0-100 cm soils.