Synergistic effects of arbuscular mycorrhizal fungi and mycorrhizae helper bacteria on soybean growth, carbendazim residues and the composition of the bacterial community in soybean rhizosphere soil

Arbuscular mycorrhizal fungi (AMF) and mycorrhizal helper bacteria (MHB) contribute substantially to suppressing pathogenic microbes, stimulating crop development, enhancing crop productivity, and optimizing the composition of the bacterial community in the rhizosphere soil. In this study, the effects of AMF and/or MHB inoculation and carbendazim application on AMF colonization rate, AMF spore density, soybean root rot disease index, soybean biomass, carbendazim residues, and the composition of the bacterial community in soybean rhizosphere soil were investigated through pot experiments. The results indicated that inoculation with AMF and/or MHB could significantly increase the AMF colonization rate and soybean biomass, reduce the root rot disease index and carbendazim residues, and alter the composition of bacterial community in soybean rhizosphere soil. Compared with the control group, the mixed inoculation treatment group showed the highest underground fresh weight, soybean yield per plant, 100-grain weight, and total bacterial colonies, with increases of 152.14%, 37.41%, 33.09%, and 23.53%, respectively. The root rot disease index, carbendazim residues in the soybean rhizosphere soil and seeds in the mixed inoculation treatment group decreased by 52.88%, 83.32% and 68.22%, respectively. Furthermore, the relative abundance of Verrucomicrobiota in the treatment group inoculated with AMF and MHB increased by 85.59% and the relative abundance of Actinomycetota was the highest in the treatment group inoculated with AMF, MHB, Fusarium oxysporum and carbendazim spraying. These findings provide a scientific theoretical foundation and practical basis for the development of efficient microbial agents that promote crop growth, enhance crop disease resistance and reduce the hazards of carbendazim residues.