Peat-based soil amendments enhance long-term soil-plant-microbe recovery in boreal mine reclamation

Soil amendment strategy is a primary determinant of long-term soil-plant-microbe recovery indicators following open-pit mining in boreal landscapes, yet evidence-based guidance for amendment selection remains limited. We conducted a nine-year field experiment at the Detour Lake Mine, Ontario, Canada, testing eight amendment strategies including peat-based combinations, inorganic fertilizer, biosolids, and oats applied singly or in combination. Peat-based treatments consistently outperformed other strategies, maintaining four-to six-fold higher soil carbon and nitrogen and supporting substantially greater vegetation structural development by Year 9 (biosolid + peat: 175.4 cm woody height, 100% vegetation cover; peat + fertilizer: 162.0 cm), compared to non-peat treatments that achieved high early cover but limited long-term woody growth. Oats with fertilizer followed an intermediate trajectory, with microbial communities showing partial compositional similarity to peat-based treatments by Year 9, though extended monitoring and supplementary organic inputs would be required where peat is unavailable. Piecewise structural equation modelling revealed that associations among soil properties, microbial communities, and vegetation shifted substantially across recovery stages, with indirect microbially associated pathways most prominent at Year 2 and direct soil-plant associations becoming more prominent by Year 9, though alternative model structures could generate similar path configurations. Treatment differences in soil resources, inferred microbial functional potential, and vegetation structure were most strongly integrated at Year 5, identifying mid-recovery as the most informative monitoring window. These findings support a trajectory-based approach to boreal mine reclamation in which combined organic and nutrient amendments support the most sustained soil, vegetation, and microbial community recovery trajectories across the indicators measured here, and repeated monitoring across recovery stages, integrating soil, microbial, and vegetation indicators, is needed to capture divergent recovery pathways and inform adaptive management decisions.