Arbuscular mycorrhizal fungi combined with mycorrhizal helper bacteria synergistically enhance cadmium stress resistance of cucumber seedlings and change soil bacterial community.

This study examines whether the mycorrhizal helper bacterium (MHB) Alcaligenes faecalis can enhance the cadmium resistance conferred by the arbuscular mycorrhizal fungus (AMF) Funneliformis mosseae in cucumbers. We evaluated plant growth, nutrient status, and rhizosphere microbiota across four treatments: non-inoculated control (CK), single inoculation of AMF (F), single inoculation of MHB (S), and co-inoculation of AMF and MHB (FS). Compared with the other three treatments, the FS treatment not only significantly increased the contents of N, P, and K in the plants, but also significantly increased the contents of soil nitrate N, available P, and available K. Moreover, the F, S and FS treatments have significantly decreased root Cd concentration and Cd content in the rhizosphere soil compared with the CK treatment. Different inoculation treatments have changed the relative abundance, composition and diversity of cucumber rhizosphere bacterial community. The F, S and FS treatments significantly increased Chao 1, Simpson index and number of OTUs compared with the CK treatment. The relative abundances of soil bacteria such as Ramlibacter, Mitsuaria, Flavisolibacter, Lysobacter, Sphingomonas and Massilia in the FS treatment were significantly higher than those in the other three treatments. Overall, our findings suggest that FS treatment enhances the resistance of cucumber seedlings to Cd stress, and this effect may be associated with changes in the rhizosphere microbial community, activation of soil nutrients, and enhanced plant nutrient uptake.