A Preliminary Edaphic and Microbial Soil Assessment to Guide the Conservation Translocation of Cytisus aeolicus in the Aeolian Islands

Cytisus aeolicus Guss. is a flagship endangered legume of the Aeolian archipelago (Italy), currently persisting in the wild only on the islands of Stromboli and Alicudi, while repeated reintroduction attempts on Vulcano Island have shown limited success. To investigate whether edaphic and microbial factors may influence habitat suitability and reintroduction success, we combined soil physicochemical characterization with 16S rRNA metabarcoding and qPCR functional validation to compare potential reintroduction sites on Vulcano with natural sites on Stromboli. Soils differed markedly between islands, showing on Vulcano higher clay and silt fractions, greater organic carbon (C) content, and higher concentrations of exchangeable calcium, potassium, and magnesium, together with enrichment in several metals. On Stromboli, soils were sandier, poorer in organic matter, and more mineral. Vulcano soils were enriched in taxa commonly associated with oligotrophic and stable environments, whereas Stromboli soils showed a greater abundance of plant growth-promoting and nitrogen-transforming microorganisms, including ammonia-oxidizing archaea potentially linked to active nitrogen and nutrient cycling in nutrient-deficient volcanic soils. Functional predictions further suggested contrasting microbial ecological strategies between islands. Overall, our results indicate that differences in soil geochemistry and microbial assembly patterns may influence the reintroduction success of C. aeolicus on Vulcano. These findings provide a first ecological framework for integrating soil processes into evidence-based conservation planning and future reintroduction strategies for this relict endemic species.