Effects of Spartina alterniflora invasion on spatial distribution of dissolved organic carbon in salt marsh soils of the Yellow River Estuary, China

Spartina alterniflora, the most widely distributed alien species in coastal wetlands of China, has caused profound effects on the elemental cycles in coastal salt marshes. A sampling belt was selected in a typical distribution zone of Spartina alterniflora in the Yellow River Estuary, which was perpendicular to a tidal creek, including continuous ribbon zone, patch zone of Spartina alterniflora, bare land and a mixed zone of Spartina alterniflora and Suaedasalas. Soil samples were collected from soil profiles with three replicates at different intervals in each of the selected four sampling zones, and soil DOC and physi-chemical properties were measured to investigate the effects of Spartina alterniflora invasion on spatial distribution of DOC. Our results showed that DOC contents in upper soils (0-20cm) and deeper soils (20-100cm) in soil profiels ranged from 5.68 to 112.17 mg/kg and from 4.27 to 94.28 mg/kg, respectively. Spartina alterniflora invasion significantly increased DOC contents in the upper soils (P< 0.05), and a decreasing trend of DOC levels was observed along the sampling belt. With the expect of patch zone, DOC contents decreased gradually with depth along soil profiles. Spearman correlation analysis indicated a strong positive correlation between DOC and soil organic carbon (P <0.05) and clay content(P <0.01), while DOC was significantly negatively corrected with pH(P <0.01). Multivariate analysis showed that there were different relationships between DOC and soil physical-chemical properties in upper and deeper soils. This study suggests that the distribution characteristic of soil DOC can be altered after Spartina alterniflora invasion, which can provide a basic knowledge about the carbon cycles in coastal salt marshes.