Mechanisms of biochar assisted di-2-ethylhexyl phthalate (DEHP) biodegradation in tomato rhizosphere by metabolic and metagenomic analysis.

The intensive accumulation of di-2-ethylhexyl phthalate (DEHP) in agricultural soils has resulted in severe environmental pollution that endangers ecosystem and human health. Biochar is an eco-friendly material that can help in accelerating organic pollutant degradation; nevertheless, its roles in enhancing DEHP removal in rhizosphere remain unclear. This work investigated the impacts of biochar dosage (0%-2.0%) on DEHP degradation performance in tomato rhizosphere by comprehensively exploring the change in DEHP metabolites, bacterial communities and DEHP-degrading genes. Our results showed a significant increase of rhizosphere pH, organic matter and humus by biochar amendment, which achieved a satisfactorily higher DEHP removal efficiency, maximally 77.53% in treatments with 1.0% of biochar. Biochar addition also remarkably changed rhizosphere bacterial communities by enriching some potential DEHP degraders of Nocardioides, Sphingomonas, Bradyrhizobium and Rhodanobacter. The abundance of genes encoding key enzymes (hydrolase, esterase and cytochrome P450) and DEHP-degrading genes (pht3, pht4, pht5, benC-xylZ and benD-xylL) were increased after biochar amendment, leading to the change in DEHP degradation metabolism, primarily from benzoic acid pathway to protocatechuic acid pathway. Our findings evidenced that biochar amendment could accelerate DEHP degradation by altering rhizosphere soil physicochemical variables, bacterial community composition and metabolic genes, providing clues for the mechanisms of biochar-assisted DEHP degradation in organic contaminated farmland soils.