Morphophysiological, biochemical, and nutrient response of spinach (Spinacia oleracea L.) by foliar CeO₂...

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 (CeO₂ NPs) at optimum concentration could significantly influence plant morpho-physiology and nutritional status. However, it remains unclear how elevated CO₂ and CeO₂ NPs interactively affect plant growth and quality. Accordingly, the ultimate goal was to reveal whether CeO₂ NPs could alter the impact of elevated CO₂ 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 CeO₂ NPs (0, 25, 50, 100 mg/L) in open-top chambers (400 and 600 CO₂ μmol/mol). Results showed that elevated CO₂ 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 CeO₂ NPs (100 mg/L) under elevated CO₂. Elevated CO₂ resulted in a decreased stomatal conductance (gs) and transpiration rate (Tr), whereas CeO₂ NPs enhanced these parameters. No significant changes were observed in any of the measured biochemical parameters due to increased levels of CO₂. However, an increase in antioxidant enzymes, particularly in catalase (CAT; 14.37%) and ascorbate peroxidase (APX; 10.66%) activities, was observed in high CeO₂ NPs (100 mg/L) treatment under elevated CO₂ levels. Regarding plant nutrient content, elevated CO₂ significantly decreases spinach roots and leaves macro and micronutrients as compared to ambient CO₂ levels. CeO₂ NPs, in a dose-dependent manner, with the highest increase observed in 100 mg/L CeO₂ 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 CO₂. Overall, CeO₂ NPs improved spinach growth and biomass and reverted the adverse effects of elevated CO₂ on its nutritional quality. These findings indicated that CeO₂ NPs could be used as an effective approach to increase vegetable growth and nutritional values to ensure food security under future climatic conditions.