n-Alkane Gradients Reshape Soil Microbial Networks and Functions at Petroleum Refinery Sites

Petroleum refining activities exert substantial contamination pressure on soil ecosystems, yet the corresponding microbial response mechanisms remain insufficiently understood. This study integrates source apportionment, high-throughput sequencing and co-occurrence network analysis to elucidate microbial adaptations along a petroleum exposure gradient. Source analysis confirmed that all soils were predominantly influenced by petroleum-derived inputs, with hydrocarbon concentrations increasing significantly across gradients. Under contamination levels of 422.35-621.21 mg/kg, petroleum pollution not only reduced soil total organic carbon (TOC) but also induced coupled C-N interactions and altered soil physicochemical properties, resulting in complex environmental effects. The soil quality index (SQI) exhibited a nonlinear trend, first decreasing and then increasing, with moderate overall levels (0.40-0.45). Functional diversity analyses indicated functional convergence rather than loss under contamination stress. At the metabolic level, low exposure primarily stimulated naphthalene degradation and detoxification pathways, whereas high exposure shifted microbial functions towards oxidative stress resistance and membrane structural remodelling. Meanwhile, microbial networks transitioned from densely connected but disturbance-sensitive structures at low exposure to simplified yet more stable and robust configurations at high exposure. These findings provide mechanistic insights into microbial adaptation in petroleum-contaminated soils and offer theoretical support for bioremediation strategies.