Microbiome restructuring by integrated ryegrass and earthworms accelerates 4-nitrophenol bioremediation in soil

4-Nitrophenol (4-PNP) is a persistent and ubiquitously distributed industrial pollutant, whose recalcitrance and inhibitory effects on microbial activity impose protracted threats to soil health in the absence of effective remediation strategies. Nevertheless, the interactive mechanisms underlying combined ryegrass-earthworm remediation remain insufficiently elucidated. Herein, we demonstrate that the joint application of ryegrass and earthworms significantly enhances the bioremediation of 4-PNP in contaminated soil. Pot experiment results revealed that the composite treatment achieved a remarkable degradation rate of 82.60% at 40 days, corresponding to a 14.4% increase relative to the indigenous microbial treatment group. The combination operated via complementary pathways: root-derived inputs from ryegrass continuously supplied organic carbon, as corroborated by increased soil organic matter, while earthworm bioturbation enhanced soil aeration, manifested as elevated oxidation-reduction potential. Collectively, these modifications optimized the microhabitat for microbial degradation. This interplay sustained urease activity at 68% of its initial level, elevated catalase activity by 18%, and elicited a distinct mid-phase peak in β-glucosidase activity (125 μg/g/h). Earthworms further augmented bacterial diversity and enriched key degrader taxa, including Sphingomonas and Bacillus. Soil moisture critically governed this process; high moisture suppressed β-glucosidase activity, implying a metabolic shift that subsequently structured the microbial community. The combined system coordinately optimized the temporal dynamics of enzyme activities and microbial composition. Collectively, these findings suggest that ryegrass-earthworm interactions are associated with 4-PNP degradation through multifaceted regulation of the soil environment, offering an actionable framework for the remediation of organic pollution.