Insights on the response of microbial communities to vegetation and biogeochemical properties in amended and unamended acid-generating mine wastes

Understanding the structure of microbial communities in acidic, metal contaminated tailings and waste rock in cool, continental northern temperate climates is important for identifying their potential for use in phytostabilization and bioremediation programs. In this study, microbial community compositions across two large mine waste sites in the Sudbury basin were analyzed along gradients of barren-to-vegetated tailings and waste rock. Microbial communities were less diverse, more homogenous, and mainly chemolithoautotrophic in barren sites, transitioning to more diverse communities of organoheterotrophs, nitrogen-fixing/plant-growth promoting bacteria, and ectomycorrhizal fungi in the vegetated areas. Network interaction analyses of microbial communities demonstrated higher levels of interactions of microbial groups in the barren tailings, which were related to the extreme environmental and chemical conditions and restricted anabolic nutrient availability of the substrates. We also show that vegetation and plant-derived organic matter in the tailings are associated with the shifts observed in the structure of microbial communities towards more soil-like communities, which sequentially further aids in the establishment of vegetation. These findings have implications for the optimization of phytoestablishment and bioremediation in mine tailings and waste rock in the cool, continental northern temperate and boreal climates.