Effects of Willow and Pine tree growth in bacterial abundance, interactions and metabolic profile in a copper mine tailing

Abstract

The Cauquenes tailings is one of the largest mine tailings in Chile and represents a significant environmental hazard due to its high copper levels and acidic pH. However, there is evidence of willow and pine tree growth in these terrains, which is unexpected given the extreme conditions of this environment. Considering the importance of plants in restoration strategies, the objective of this study was to analyze the effect that willow and pine growth have on the heavy metal contents of their surrounding soil, and the abundance, interaction, metabolic profile and assembly of the bacterial community. In the Cauquenes tailing, we collected samples from willow and pine vegetated soils as well as the surrounding non-vegetated soils. We analyzed characteristics such as heavy metal concentrations and pH levels in all sampled soils, and in tree leaves and roots. Vegetated sites exhibited lower copper levels and a neutral pH, while both tree species accumulated heavy metals in their tissues. We also determined bacterial abundance in all soil samples, and co-occurrence networks were constructed to assess bacterial interactions. Both trees promoted a higher abundance of Proteobacteria and had networks with higher modularity compared to non-vegetated soils. Finally, we estimated the metabolic profile of the bacterial community using PICRUSt 2 analysis and determined carbon source utilization with BioLog Ecoplates. PICRUSt 2 predicted higher metabolic activity in vegetated soils, and BioLog Ecoplate analysis revealed the utilization of a greater number of carbon sources. The microbial communities from vegetated soils were assembled in a deterministic manner, while the community from non-vegetated soils were stochastically assembled. In conclusion, tree growth mitigated the extreme conditions of the tailing and promoted a more active and healthier bacterial community. HighlightsO_LIWillow and pine tree can grow and mitigate toxic metal conditions in the tailings C_LIO_LIBoth trees provoked a shift in bacterial abundance and interaction network C_LIO_LIThe provoked shift was tree-dependent C_LIO_LIMicrobial activity was higher in vegetated soils C_LI