Windstorm disturbance sets off plant species invasion, microbiota shift, and soilborne pathogens spread in an urban Mediterranean forest

We investigated the effects of a severe windstorm on vegetation, soil chemistry, understory microclimate, and soil microbiota in a Mediterranean holm oak forest. Plant species composition remained almost unchanged in the undisturbed area, whereas highly diverse plant communities were found in the disturbed area (e.g. gap area). Specifically, 11 invasive plant species were detected in 2015, but four years after, five disappeared and another five decreased, with only Ailanthus altissima increasing. Soil in disturbed areas has higher pH, Na, P, K, Ca, Cu, and Mn, but lower total limestone, organic carbon, total nitrogen, Mg, Fe, and standing litter compared to undisturbed areas. Disturbed areas had higher light availability at the ground and large variations in soil and air temperature and air relative humidity compared to undisturbed areas. The storm disturbance increased soil bacterial and fungal species richness and diversity. Moreover, the microbial co-occurrence network in the undisturbed area was more heterogeneous and complex, while modularity and number of positive correlations were higher in the disturbed area, which suggests that the structural composition of microbial communities and their co-occurrence patterns have been altered by windstorm disturbance. In the gaps, soil microbial community composition indicated a shift toward an opportunistic microbiota dominated by fast-growing but less competitive species. In addition, we found a large increase in putative plant pathogens but a decrease in simbiotrophic and ectomycorrhizal fungi in the gaps. The present work demonstrate the multiple effects of storm damage on the above- and belowground structure and diversity of forest ecosystems.