Above- and belowground impacts of Spartina patens invasion in mediterranean salt marshes: Ecological insights and management priorities

Biological invasions in coastal ecosystems can cause cascading impacts on biodiversity, ecosystem functioning, and restoration success. This study investigates the invasion dynamics of Spartina patens in the salt marshes of the Albufera Natural Park (Spain), focusing on its effects on native plant communities and soil microbial assemblages. We conducted cartographic mapping, vegetation inventories, and soil/root sampling across five marshes. Plant communities were assessed using the Braun-Blanquet method, whereas fungal and bacterial communities were characterised through high-throughput sequencing of the ITS and 16S rDNA regions. Arbuscular mycorrhizal fungi (AMF) presence in roots was quantified microscopically. A two-phase colonisation pattern is suggested: initial establishment along marsh boundaries followed by vegetative expansion into interior zones. This spatial dynamic establishes edge habitats as critical zones for early detection and control. Spartina patens significantly reduced native plant diversity by forming dense, dominant stands that simplified habitat structure and displaced endemic species. While fungal richness remained stable across zones, showed a tendency to be higher at marsh boundaries, likely reflecting environmental variability during early invasion stages. A positive correlation between fungal and bacterial richness suggests a synergistic microbial network contributing to ecosystem processes. Spartina patens showed strong associations with AMF, supporting greater AMF richness than native grasses. These symbioses may enhance its competitive advantage by improving nutrient uptake and stress tolerance, while disrupting native plant–microbe interactions. Our findings underscore the importance of integrating above- and belowground data in invasion ecology. We propose recommendations for early intervention, microbial monitoring, and adaptive restoration planning to support biodiversity and ecosystem resilience.