Pinaceae-EMF symbiosis drives soil organic carbon heterogeneity in tropical mining ecosystem restoration

While broad environmental drivers (e.g., climate variation or nitrogen deposition) modulate carbon dynamics in intact ecosystems, open-pit mining represents a catastrophic disturbance that strips topsoil, destroys soil structure, and imposes acute phosphorus (P) limitation, creating extreme bottlenecks for plant-microbe-mediated soil carbon recovery. Here, we compare soil organic carbon (SOC) concentration dynamics and stabilization patterns of ectomycorrhizal Pinaceae and nitrogen-fixing Fabaceae stands across post-mining restoration stages in Santa Lucía (Cuba) and Hainan (China) using metagenome analyses. Leaf nutrient resorption analysis revealed NRE/PRE consistently below 1 in both regions, indicating phosphorus as the primary limitation. Against this shared phosphorus-limited backdrop, we asked whether Pinaceae-EMF symbioses promote SOC restoration through local EMF attributes, including α-diversity and relative abundance, or through among-stand compositional turnover. Pinaceae consistently increased EMF diversity, but elevated SOC concentrations and EMF abundance occurred only in Cuba's flat plains, showing positive correlations with SOC stocks. In Hainan's rolling hills, diversity recovery decoupled from abundance accumulation. Although α-diversity correlated with carbon stocks, EMF relative abundance showed no association with any carbon pool, indicating that diversity alone did not drive carbon accumulation, paralleling slower carbon recovery. We therefore evaluated EMF β-dissimilarity as a landscape-scale metric linking fungal community turnover to SOC heterogeneity across restoration landscapes with contrasting connectivity. These divergent local-scale relationships indicate that neither EMF α-diversity nor abundance alone predicts SOC across divergent restoration trajectories. Consequently, we tested whether EMF community heterogeneity (β-dissimilarity) provides a more robust predictor of carbon variation. Results showed that microbial β-dissimilarity consistently predicted SOC variation across both regions, suggesting that community-level functional turnover and niche differentiation across restoration stages rather than simple biomass accumulation primarily correlate with POC and MAOC dynamics.These findings highlight that overcoming phosphorus limitation through EMF-mediated strategies, particularly community heterogeneity, provides essential means for carbon restoration across tropical mining ecosystems with contrasting landscape connectivity.