Patterns and microbial drivers of 4-nitrophenol natural attenuation in black soil versus yellow-brown soil

As a toxic industrial intermediate, 4-Nitrophenol (4-PNP) poses severe ecological and health risks. However, the microbial mechanisms governing its biodegradation under natural attenuation remain elusive, constraining accurate fate prediction. This study employed a mesoscale sandbox model to compare the metabolic degradation processes of 4-nitrophenol (4-PNP) under simulated rainfall environment in black soil (high fertility, high porosity) and yellow-brown soil (low nutrient content, compacted). Results indicate that physical structure determines pollutant distribution, black soil exhibits rapid vertical migration, whereas yellow-brown soil displays a rapid degradation-local retention pattern. Mechanistically, microorganisms in nutrient-poor yellow-brown soil achieve 4-PNP mineralisation through specific upregulation of the fadA gene, a process constrained by functional microbial communities (e.g., Sphingomonas) and enzymatic activity. Conversely, in fertile black soil, endogenous carbon induces suppression of carbon degradation metabolism, prompting microorganisms to prioritise degrading easily decomposable organic matter. This leads to degradation processes being impeded by community resource competition. Structural equation modelling validation indicates that black soil's self-purification capacity is synergistically driven by abiotic factors and genes, whereas yellow-brown soil is primarily regulated by environmentally driven functional microbial community selection mechanisms. The soil-specific metabolic strategy model revealed in this study provides a theoretical basis for precision remediation of heterogeneous sites.