Nanoselenium and Melatonin Diminish Bensulfuron-methyl Toxicity in Field Wheat by Regulating Interaction among Rhizosphere Soil Allelochemicals, Bacterial Community, and Plant Metabolites

The crop yield loss and quality decline due to herbicides' unreasonable application seriously threaten global food security. Nanoselenium (nano-Se) and melatonin have been shown to improve plants' tolerance to abiotic stress. Here, this study investigated the effects of nano-Se and melatonin on wheat growth, metabolism, and resistance under bensulfuron-methyl stress through field experiment. Nano-Se and melatonin application activated the indole alkaloid metabolism and increased the contents of tryptamine, 5-hydroxytryptamine, DIMBOA-Glc, and HDMBOA-Glc in leaves, roots, rhizosphere soil, and grains at different wheat growth stages. This increased wheat height (22.3%) and the weight of thousand grains (8.1%) when exposed to bensulfuron. The contents of allelochemicals (jasmonic acid and DIMBOA-Glc), microbial communities (<i>Alphaproteobacteria</i>, <i>Gammaproteobacteria</i>, <i>Bacteroidia</i>, and <i>Gemmatimonadetes</i>), and soil-lipase (21.3%), and soil-fluorescein diacetate (16.4%) were also significantly increased by nano-Se and melatonin biofortification during the wheat ripening stage under bensulfuron treatment. Changes in microbial communities were closely linked to the plant metabolites and soil allelochemicals (benzoxazinoids (BXs)), which promoted wheat growth and lessened the harmful effects of bensulfuron-methyl. In summary, nano-Se and melatonin might reduce phytotoxicity by promoting plant metabolism (BXs) and improving the soil microenvironment and signal transduction in the rhizosphere soil and wheat plants.