Spontaneous vegetation colonizing abandoned metal(loid) mine tailings consistently modulates climatic, chemical and biological soil conditions throughout seasons.

This study aimed to evaluate whether the improvement in soil conditions induced by the vegetation spontaneously colonizing abandoned metal(loid) mine tailings from semiarid areas is consistent throughout seasons and to identify if the temporal variability of that conditions is of similar magnitude of that of the surrounding forests. Soil climatic (temperature and moisture), chemical (pH, electrical conductivity and water-soluble salts and metal(loid)s) and biological (water-soluble organic carbon and ammonium, microbial biomass carbon, dehydrogenase and β-glucosidase activity, organic matter decomposition and feeding activity of soil dwelling organisms) parameters were seasonally evaluated for one year in bare soils and different vegetated patches within metalliferous mine tailings and surrounding forests in southeast Spain. The results indicated that the improvement in soil conditions (as shown by softening of climatic conditions and lower scores for salinity and water-soluble metals and higher for biological parameters) induced by vegetation colonization was consistent throughout seasons. This amelioration was more evident in the more complex vegetation patches (trees with herbs and shrubs under the canopy), compared to bare soils and simpler soil-plant systems (only trees), and closer to forest soils outside the tailings. Bare soils and, to a lesser extent, vegetation patches solely composed by trees, showed stronger seasonal variability in temperature, moisture content, salinity, and water-soluble metals. In contrast, changes in biological and biological-related parameters were more pronounced in the more complex vegetation patches within mine tailings and surrounding forests due to its greater biological activity. In summary, the results demonstrated that vegetation patches formed by spontaneous colonization act as microsites that modulate seasonal variability in soil conditions and stimulate biological activity. This suggests that tailings vegetation patches might have higher resilience against climate change effects than bare soils. Therefore, they should be preserved as valuable spots in the phytomanagement of metal(loid)s mine tailings from semiarid areas.