Long-term Spartina alterniflora invasion simplified soil seed bank and regenerated community in a coastal marsh wetland.

The coastal wetland is easily invaded by alien species due to locating in the land and sea transitional area. As a potential driving regeneration force, the soil seed bank is vital to the community restoration and species diversity protection. To reveal the long-term Spartina alterniflora invasion impact on the soil seed banks and regenerated communities, we investigated the seed banks under the different vegetation types (S. alterniflora, Phragmites australis, Scirpus mariqueter, ruderal and unvegetated site) and soil depths (0-5 and 5-10 cm) in the coastal salt marsh wetland, Chongming island, eastern China. The results showed that the soil seed bank richness and species density under different vegetation types were higher than the aboveground vegetation, and those of 0-5 cm seed banks were higher than 5-10 cm, except for the unvegetated site. The species richness and S. alterniflora seed proportion in the seed banks under S. alterniflora communities (S.AS) were lower and larger respectively than those of other sites. The species composition between S.AS and the aboveground communities showed high similarity with aggregation phylogenetic structures in two soil depths. The seed bank variations at 0-5 and 5-10 cm depths were interpreted 3.03% and 2.25% by the aboveground communities, while 4.92% and 5.55% were interpreted by the soil microbial biomass. The SEM model explained 98.1% and 91.8% of the seed banks richness at the 0-5 cm depth and 5-10 cm depth, respectively, and explained 98.8% and 46.1% of the seed banks species density at the 0-5 cm depth and 5-10 cm depth, respectively. The aboveground vegetation biomass and abundance directly affected the 0-5 cm seed banks richness and species density, while its height and biomass only affected the 5-10 cm seed banks species density. The 0-10 cm soil depth microbial biomass indirectly affected the 0-5 cm seed banks richness and species density, while affected the 5-10 cm seed banks richness. Soil physical and chemical properties only indirectly affected the 0-5 cm seed banks species density. The results provided a reference for the ecological evaluation of the impacts of S. alterniflora invasion into the coastal salt marsh wetland of eastern China, and guidance for the protection and restoration of the native plant communities.