Abstract:

The aim of this work was to determine whether treatment with cerium dioxide nanoparticles （CeO₂ NPs） increases the salt tolerance of alfalfa （Medicago sativa）. A 50 mg·L^-1 solution of CeO₂ NPs was applied by foliar spraying to ‘Zhongmu No.1’ alfalfaseedlings， and the seedlings were then subjected to a 10-day salt stress treatment with 300 mmol·L^-1 NaCl. A range of parameters， including growth， photosynthetic characteristics， membrane lipid peroxidation， antioxidant enzyme activities， and osmotic regulatory substance contents were measured to comprehensively evaluate the effect of CeO₂ NPs on the salt tolerance of alfalfa plants. Salt stress significantly inhibited seedling growth， reduced biomass， and photosynthetic capacity， and increased reactive oxygen species accumulation. When plants in the control group and those sprayed with CeO2 NPs were subjected to the salt treatment， those in the treatment group showed significantly milder symptoms of salt damage， increased seedling growth and biomass accumulation， and higher relative water content and photosynthetic performance. Under salt stress， the plants sprayed with CeO₂ NPs exhibited significantly reduced relative conductivity， malondialdehyde content， and hydrogen peroxide and superoxide anion accumulation， and elevated activities of superoxide dismutase （SOD）， ascorbate peroxidase （APX）， catalase （CAT）， and peroxidase （POD）， as well as increased soluble sugar and proline contents. Specifically， in the CeO₂ NPs-treated plants compared with control plants， the SOD， APX， CAT， and POD activities were increased by 20.0%， 29.9%， 41.4%， and 54.3%， respectively， while the soluble sugar and proline contents were increased by 39.4% and 16.5%， respectively， under salt stress. Collectively， these results show that CeO₂ NPs promote photosynthesis and growth by enhancing antioxidant enzyme activities， promoting the accumulation of osmoprotectants， and decreasing oxidative damage， thereby enhancing alfalfa’s salt tolerance.

Key words: cerium dioxide nanoparticles, salt stress, alfalfa, photosynthetic changes, physiological response