Divergent invasive and native wetland plant microbial community responses to estuarine wetland salinity gradients

The invasion of non-native species such as Spartina alterniflora threatens estuarine wetland ecosystems. Understanding how salinity influences the root and rhizosphere microbial communities remains limited. This study investigated the impacts of natural estuarine salinity gradients on root and rhizosphere microbial communities in invasive S. alterniflora versus native Phragmites australis. S. alterniflora exhibited pronounced rhizosphere nutrient advantages under both low- and high-salinity conditions, particularly in high-salinity environments. Both plant species maintained stable bacterial and fungal diversity and richness within root endospheres. Notably, fungal richness in S. alterniflora roots was correlated with pH, available nitrogen (AN), and available potassium (AK), whereas P. australis demonstrated no associations between fungal parameters (diversity and richness) and soil properties, suggesting a stronger coupling between the endophytic fungi in S. alterniflora and rhizosphere pH and nutrient status. Rhizospheric bacterial richness and diversity displayed minimal interspecific differences under low-moderate salinity, but marked differences emerged under high salinity, revealing salinity-dependent bacterial community differentiation linked to plant species. Both species had similar effects on rhizospheric fungi, and showed no apparent salinity tolerance advantage in the fungal communities of S. alterniflora. Salinity- mediated alterations in microbial network complexity displayed plant species-specific patterns. Our study underscores the crucial role of microbial communities in the successful invasion of S. alterniflora and offers valuable insights for managing and restoring estuarine wetlands.