Morphophysiological, biochemical, and nutrient response of spinach (Spinacia oleracea L.) by foliar CeO nanoparticles under elevated CO.

Nanomaterials offer considerable benefits in improving plant growth and nutritional status owing to their inherent stability, and efficiency in essential nutrient absorption and delivery. Cerium oxide nanoparticles (CeO NPs) at optimum concentration could significantly influence plant morpho-physiology and nutritional status. However, it remains unclear how elevated CO and CeO NPs interactively affect plant growth and quality. Accordingly, the ultimate goal was to reveal whether CeO NPs could alter the impact of elevated CO on the nutrient composition of spinach. For this purpose, spinach plant morpho-physiological, biochemical traits, and nutritional contents were evaluated. Spinach was exposed to different foliar concentrations of CeO NPs (0, 25, 50, 100 mg/L) in open-top chambers (400 and 600 CO μmol/mol). Results showed that elevated CO enhanced spinach growth by increasing photosynthetic pigments, as evidenced by a higher photosynthetic rate (Pn). However, the maximum growth and photosynthetic pigments were observed at the highest concentration of CeO NPs (100 mg/L) under elevated CO. Elevated CO resulted in a decreased stomatal conductance (gs) and transpiration rate (Tr), whereas CeO NPs enhanced these parameters. No significant changes were observed in any of the measured biochemical parameters due to increased levels of CO. However, an increase in antioxidant enzymes, particularly in catalase (CAT; 14.37%) and ascorbate peroxidase (APX; 10.66%) activities, was observed in high CeO NPs (100 mg/L) treatment under elevated CO levels. Regarding plant nutrient content, elevated CO significantly decreases spinach roots and leaves macro and micronutrients as compared to ambient CO levels. CeO NPs, in a dose-dependent manner, with the highest increase observed in 100 mg/L CeO NPs treatment and increased roots and shoots magnesium (211.62-215.49%), iron (256.68-322.77%), zinc (225.89-181.49%), copper (21.99-138.09%), potassium (121.46-138.89%), calcium (118.22-91.32%), manganese (133.15-195.02%) under elevated CO. Overall, CeO NPs improved spinach growth and biomass and reverted the adverse effects of elevated CO on its nutritional quality. These findings indicated that CeO NPs could be used as an effective approach to increase vegetable growth and nutritional values to ensure food security under future climatic conditions.