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 its location
in the land and sea transitional area. As a potential driving regeneration
force, the soil seed bank is vital to community restoration and species
diversity protection. To reveal the long-term S. 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 mariquete, ruderal and unvegetated site) and
soil depths (0–5 cm and 5–10 cm) in the Chongming island coastal salt
marsh wetland. The results showed that the soil seed bank richness and
species density under different vegetation types were higher than
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 the S.
alterniflora seed proportion in the seed banks under the S. alterniflora
communities (S.AS) were lower and larger, respectively, than 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 cm and 5–10 cm depths were
interpreted 3.03% and 2.25% by aboveground communities, while 4.92% and
5.55% were interpreted by 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 microbial biomass of the 0–10 cm soil depth indirectly
affected the richness and species density of the 0-5 cm seed bank, and
only affected the richness of the 5–10 cm seed bank. 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.