Soil salinization is an increasingly severe global issue, posing a significant threat to crop growth and food security. Although sorghum exhibits moderate tolerance to saline-alkali stress, it remains highly sensitive to such conditions during the seedling stage. This study investigates the mechanisms by which zinc oxide nanoparticles (ZnO NPs) alleviate saline-alkali stress in sorghum seedlings and determines their optimal application concentration, thereby providing a scientific basis for agricultural production in saline-alkali soils. Hydroponic experiments were conducted to simulate varying degrees of saline-alkali stress. Sorghum seedlings were treated with different concentrations of ZnO NPs (0, 50, 100, 200 mg·L−1). The efficacy of ZnO NPs was comprehensively evaluated by measuring biomass, chlorophyll content, antioxidant enzyme activities, non-enzymatic antioxidant levels, sodium and potassium ion distribution, and lipid peroxidation. These physiological assessments were further supported by correlation analysis, principal component analysis (PCA), and response surface methodology (RSM). The results indicate that ZnO NPs maintain intracellular redox homeostasis by inhibiting the degradation of photosynthetic pigments, enhancing the synergistic interactions between enzymatic and non-enzymatic antioxidants, and preserving ionic equilibrium. These mechanisms effectively suppress malondialdehyde accumulation, protect membrane integrity, and improve seedling resilience to stress. Furthermore, PCA and RSM revealed that the optimal ZnO NPs concentration is approximately 100 mg·L−1. Excessive concentrations, however, exert toxic effects and inhibited seedling growth. Overall, this study highlights the potential of applying ZnO NPs as nano-fertilizers to improve crop resilience in saline-alkali soils.
Li et al. (2026) studied this question.