Omics shed light on the mechanisms of petroleum‐contaminated soil remediation: When biochar meets nitrogen.

Decontamination of oil‐affected soil is an urgent worldwide issue. In this study, a microcosm experiment was conducted to explore the effect of combined utilization of urea and biochar on oil‐contamination remediation in an eastern China oil‐field soil and explored their impact on soil physicochemical properties, organic pollutants degrading‐related enzyme and functional genes, microbiome, and metabolome. Then, a pot experiment was conducted to verify the impact of the remediation experiment. Results showed that a combined application of biochar and nitrogen reduced 78.6% of total petroleum hydrocarbons in soil. Combined treatment enhanced soil dehydrogenase and catalase activities, alkB, and CYP gene abundances relative to Control. Moreover, nitrogen input reduced soil microbial α‐diversity, while improving the relative abundances of Alcanivorax and Pseudogym. In addition, the pathways of glyoxylate and dicarboxylate metabolism, naphthalene and anthracene degradation, butanoate metabolism, pyruvate metabolism, and glycolysis or gluconeogenesis were up‐regulated in combined treatment relative to Control. Besides, both biochar and nitrogen addition can increase the number of edges and clustering coefficient of the microbial network, and improve the network robustness. The pot experiment showed that combined treatments enhanced ryegrass shoot length, root length, and biomass by 57.8%, 38.5%, and 42.8%, respectively. Overall, this study proved the feasibility of combined biochar and urea co‐application in remedying oil‐contaminated soil and shed light on the inner mechanism. [ABSTRACT FROM AUTHOR]