Strong community-level network interactions contribute to stress tolerance: interconnected microbial community responses to metals and vegetation in acid-generating mine wastes

Understanding microbial community strategies to adapt 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, the structure of microbial communities across two large mine waste sites in the Sudbury basin was 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 and soil-like communities of organoheterotrophs, nitrogen-fixing/plant-growth promoting bacteria, and ectomycorrhizal fungi in the vegetated areas. Network interaction analyses of microbial communities demonstrated more complex within-community interactions (i.e. more direct reliance of guilds upon each other) in the barren tailings, which probably exist to help the community members to cope with the extreme environmental and chemical conditions and restricted redox substrate and anabolic nutrient availability. We also show that vegetation and associated plant-derived organic matter in the tailings, can potentially ease the proliferation stress of heterotrophic microorganisms, which 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.