Invasive Plants Do Not Exert Univocal Responses on Soil Abiotic and Biotic Characteristics

Invasive plants are among the top five drivers of biodiversity loss, primarily due to competition and allelopathy. By releasing root exudates, they alter soil properties, influencing both soil abiotic and biotic characteristics. The effects of invasive plants on soil characteristics and biota remain underexplored, with findings often controversial and context-dependent. This study aimed to understand the impact of two invasive species—black locust (Robinia pseudoacacia L.) and tree of heaven (Ailanthus altissima Mill.)—on soil abiotic characteristics, microbial and Collembola com-munities. Comparisons were made with soils under two native vegetation covers, holm oak (Quercus ilex L.) and herbaceous vegetation. In fall 2023, twelve sites within Vesuvius National Park (three per plant cover) were sampled to assess soil characteristics, microbial biomass and activities, and Collembola communities. The results demonstrated that tree of heaven increased soil pH, reduced organic carbon content, but enhanced bacterial biomass and activity, and Col-lembola density, being similar to holm oak soil. In contrast, black locust increased soil nitrogen content but decreased microbial biomass and activity, and Collembola density. Despite these differences, Collembola species composition was scarcely diversified and largely similar under both invasive species. In conclusion, the presence of invasive plants was associated with declines in soil organism biodiversity, underscoring their disruptive influence on soil ecosystems.