Soil microbial communities and reactive oxygen species reshape MAOC-driven PAH accumulation under seasonal trade-offs...

Current understanding of the accumulation of polycyclic aromatic hydrocarbons (PAHs) in terrestrial ecosystems suggests that soil organic carbon (SOC) dynamics is a key regulator, including particulate- (POC) and mineral-associated (MAOC) organic carbon. This creates possible 'competition' between soil POC and MAOC for the accumulation of PAHs. However, it remains unclear to what extent seasonal SOC pool dynamics modulate the balance between cold trapping and forest filtering, especially through microscale processes linked to soil microbial communities and redox conditions. Here, we investigate the altitudinal and seasonal dependence of PAHs, SOC pools, soil properties, reactive oxygen species (ROS), and microbial communities in forest soils. Significant seasonal difference in the altitudinal pattern (spring: r = -0.68, p < 0.0001; autumn: r = 0.624, p < 0.0001) of PAHs in soils, together with relationships with altitude, logKow, and the humus/mineral-soil ratio, suggests a greater contribution from forest filtering to the springtime soil PAH concentrations and a stronger influence of cold trapping in autumn. Forest filtering increases soil PAHs concentrations and POC formation in the humus layer, but constrains MAOC accumulation. Nevertheless, the cold trapping effect promotes soil MAOC pools in autumn, thereby increasing soil PAHs concentrations. These patterns are primarily driven by the seasonal reorganization of soil physicochemical properties and microbial communities, thereby facilitating the transformation of ROS and SOC pools. Overall, these results advance our understanding of how SOC fraction dynamics, soil properties, and microbial communities jointly regulate global PAHs accumulation under a changing climate.