Topographic decoupling of tree-mortality disturbances drives contrasting soil carbon fates via divergent microbial strategies

Abstract

Climate change is exacerbating tree mortality worldwide, threatening the stability of forest soil organic carbon (SOC) stocks. However, how SOC responds to tree mortality amid co-occurring disturbances remains mechanistically unresolved. Here, we demonstrate that topography spatially decouples the canopy-opening and detrital-legacy effects of tree mortality and transforms these co-occurring disturbances into distinct selective pressures on soil microbial communities, thereby driving SOC toward contrasting fates through divergent microbial strategies for carbon and energy acquisition. On ridges, canopy-opening effects co-select for exo-enzyme and aerobic-respiration traits, alongside SOC loss associated with reduced heavy-fraction organic carbon. In valleys, detrital-legacy effects promote light-fraction-associated SOC gain while co-enriching endo-enzyme and anaerobic-respiration traits, potentially strengthening SOC retention. By integrating amplicon sequencing with genome-informed functional traits, our study provides genomic evidence for the microbial mechanisms underlying divergent SOC responses to tree mortality and highlights the potential of genome-based microbial traits for predicting ecosystem-scale biogeochemical processes. Topography spatially decouples the canopy-opening and detrital-legacy effects of tree mortality, creating distinct pressures on soil microbes that drive soil carbon toward contrasting fates through divergent microbial strategies.