Foliar Spraying of Nanoselenium Improves the Nutritional Quality of Alfalfa by Recruiting Beneficial Phyllosphere Bacteria and Regulating the Distribution and Translocation of Selenium

Nanoselenium shows potential trends in improving plant health and food quality. In this study, different concentrations of nanoselenium were sprayed on the leaves of alfalfa. Compared to the control, nanoselenium (100 mg·L^-1) significantly increased SeMet and SeMeCys contents in the roots, stems, and leaves of alfalfa. Nanoselenium educed malondialdehyde by modulating the glutamine synthetase-glutamate synthetase (GS-GOGAT) cycle and activating antioxidant enzymes, including the ascorbate-glutathione (AsA-GSH) cycle, as well as enhancing photosynthesis, resulting in an increase in the alfalfa yield, crude protein, and relative feeding value. The biofortification of nanoselenium mainly changed the community structure of phyllosphere bacteria by regulating metabolic pathways such as amino acid metabolism, carbohydrate metabolism, and membrane transport, among which Proteobacteria were more responsive to nanoselenium. In conclusion, nanoselenium will enhance photosynthesis, improve signaling molecules, and recruit beneficial bacteria to regulate the nutritional levels of alfalfa.