Soils in the Mediterranean region are affected by climatic conditions that increase the risk of organic matter depletion and desertification. Intensive land use exacerbates this susceptibility, leading to soil degradation, biodiversity loss and reduced ecosystem functionality. Organic soil amendments, rich in stable organic matter, represent a sustainable strategy for restoring degraded soils. Amendments derived from waste materials align with circular economy principles; however, an integrated assessment of their ecological effects on the soil-plant system is required. Particular attention should be given to exogenous microbial groups introduced into the soil, as they can reshape the edaphic microbial communities.

This research, conducted within the EMBRACE National Interest Project (PRIN 2022 PNRR), characterised the microbial communities associated with waste-derived amendments for ecological restoration purposes — a vermicompost made from marine waste and a sludge-based amendment, as well as their variants enriched with natural zeolites. Their effects on soil microbial communities were also investigated six months after application on amended Mediterranean soils. The study focused on spore-forming bacteria, siderophore-producing bacteria, actinomycetes, phosphorus-solubilising bacteria, and fungi. The antibiotic activity of all isolates against the phytopathogenic fungus Rhizoctonia solani was also assessed to evaluate their potential contribution to revegetation through biocontrol.

The results revealed significant differences in microbial community composition among amendments, mainly driven by their organic composition. Following soil application, these differences resulted in measurable, although less pronounced, changes in soil microbial communities. However, phosphorus-solubilising bacteria, despite being abundant in several amendments, were not detected in the amended soils. Natural zeolites reduced organic fraction effects while promoting some microbial groups. Significant differences in antibiotic activity against R. solani were observed among treatments, with promising results for spore-forming bacteria.

Overall, these findings provide valuable insights into assessing spontaneous revegetation through soil amendments in the context of ecological restoration, while offering useful information for future agronomic applications.