Synergistic interplay between Azospirillum brasilense and exogenous signaling molecule HS promotes Cd stress resistance and growth in pak choi (Brassica chinensis L.).

Inoculation with growth-promoting rhizobacteria inoculation and the addition of exogenous signaling molecules are two distinct strategies for improving heavy metal resistance and promoting growth in crops through several mechanisms. However, whether rhizobacteria and phyllosphere signaling molecules can act synergistically alleviate heavy metal stress and promote growth and the mechanisms underlying these effects remain unclear. Here, a novel strategy involving the co-application of growth-promoting rhizobacteria and an exogenous signaling molecule was developed to reduce cadmium (Cd) phytotoxicity and promote pak choi growth in Cd-contaminated soil. We found that the co-application of Azospirillum brasilense and hydrogen sulfide (HS) resulted in significant improvements in shoot biomass and antioxidant enzyme content and a decline in the levels of Cd translocation factors. In addition, this co-application significantly improved pak choi Cd resistance. Furthermore, we observed a significant negative correlation between abscisic acid concentration and Cd content of pak choi and a positive correlation between HS concentration and biomass. These findings revealed that the co-application of rhizobacteria and exogenous signaling molecules synergistically promoted the growth of vegetable crops subjected to heavy metal stress. Our results may serve as a guide for improving the food safety of crops grown in soil contaminated with heavy metals.