Remediation strategies of biochar and microbial inoculum for PAHs-contaminated soil: Quorum sensing-mediated PAHs degradation and element cycling.

The pyrolysis of straw for biochar production offers significant advantages in resource recycling and soil improvement. However, the concurrent effects of biochar on contaminant degradation and biogeochemical cycles in polycyclic aromatic hydrocarbons (PAHs)-contaminated soil remain unclear. This study aims to integrate the roles of functional microorganisms, PAHs degradation pathways, and soil element cycles to elucidate the remediation characteristics of PAHs-contaminated soil. The results demonstrated that the addition of biochar increased the removal rate of phenanthrene (PHE) of PAHs in soil by 75.7 %, and microbial inoculum enhanced this rate to 93.4 %. Both treatments simultaneously improved soil physicochemical properties. Additionally, these amendments influenced the composition of the microbial community, increasing microbial diversity as evidenced by a rise in the Chao1 index by 2.75 % and 4.50 %, and the Shannon index by 8.73 % and 7.60 %, respectively. Moreover, the addition of biochar and microbial inoculum enabled quorum sensing and key microbial species to play a significant role in PHE degradation and ecological restoration. Specifically, these amendments have altered the degradation pathways of soil PHE: biochar promoted PHE degradation via the phthalate pathway, whereas microbial inoculum favored the salicylic acid pathway. Furthermore, both amendments expedited nutrient element cycling in soils. Biochar stimulated nitrate assimilation and the degradation of labile organic carbon compounds, while microbial inoculum enhanced the biodegradation of refractory organic carbon, carbon and nitrogen fixation, and concurrently reduced greenhouse gas emissions. This study presents an innovative strategy for ecologically rehabilitating PHE-contaminated soils by integrating microbial interactions with soil element circulation.