Soil microbial communities dynamics in response to invasive groundcover Carpobrotus: Insights into native species interactions and edaphic influence

Alien invasive plant species of the genus Carpobrotus pose a major threat to coastal dune ecosystems. These human-introduced species have quickly expanded throughout the Mediterranean basin and other regions due to their high reproduction rates and adaptability. Carpobrotus invasion alters soil properties due to necromass and the release of allelopathic compounds, hindering the regrowth of native flora, with anticipated impacts on the native vegetation-associated soil microbial communities. While some studies have described changes in microbial communities between native and Carpobrotus-impacted areas, none have specifically addressed the responses of microbial communities associated with single native species. In this light, the bacterial and fungal communities specifically associated with different native species in both natural and Carpobrotus-impacted plots were examined in three locations along the middle Tyrrhenian Italian coast. Microbial communities responses to the Carpobrotus invasion varied greatly depending on the native species and the edaphic characteristics of the study locations. Microbial communities associated with Pancratium maritimum were the most affected ones and those associated with Cakile maritima the less sensitive to the invasion, which may be correlated to the different characteristics of these plant species. Furthermore, fungal communities exhibited a greater degree of disruption compared to bacterial ones. In invaded plots, fungal species that comprise plant pathogens were notably more abundant. This suggests that patterns in microbial communities response to this invasion phenomenon cannot be generalized, and that recovery strategies should consider various local conditions and be adjusted for the various native vegetation species. Finally, the possible spread of fungal plant pathogens as a mechanism of defence of Carpobrotus should be considered.