Biochar remodeled rhizosphere microbial community structure and function to alleviate sugar beet under fomesafen...

Residual fomesafen in soybean field soil can adversely affect subsequent sugar beet crops. Biochar has been shown to alleviate this damage, the regulatory mechanisms by which it influences the rhizosphere microbial community and its functions in the presence of fomesafen residues remain unclear. This study employed plant physiological assessments, amplicon sequencing, and metagenomic analysis to investigate root physiology, the rhizosphere soil microbial community, and their functional responses to fomesafen toxicity with biochar addition. By comparing sterilized soil with normal soil, that all measured indices in the sterilized soil were reduced, confirming that biochar mitigates fomesafen phytotoxicity through soil microorganisms. Biochar increased root biomass by 37.50 % under fomesafen residue stress, reduced malondialdehyde content in sugar beet roots, enhanced antioxidant enzyme activity, and improved soil multifunctionality by 13.95 %. Furthermore, biochar significantly restored the richness and diversity of rhizosphere fungi and bacteria under fomesafen residue stress. The relative abundance of Dehalococcoidia, a potential herbicide-degrading bacterium, increased significantly under fomesafen stress (90.32 %) and peaked under biochar mitigation treatment (94.02 %), suggesting its potential as a biomarker for fomesafen residues. Biochar alleviated fomesafen's impact on the microbial network, restoring it to a molecular ecological network similar to the control. Metagenomic analysis revealed that biochar increased the Calvin-Benson-Bassham cycle (29.87 %), the nitrogen fixation pathway (21.42 %), and the phosphate transport pathway (10.60 %). By enhancing soil multifunctionality and reshaping rhizosphere microbial communities, biochar improves the stress resistance of sugar beet roots and mitigates damage caused by fomesafen. This finding is significant for maintaining the microecological balance of the rhizosphere.