Foliar Application of Calcium Phosphate Nanoparticles Improves Photosynthetic Efficiency, Nutrient Uptake, and Antioxidant Capacity in <i>Coriandrum sativum</i> L. under Salinity Stress

Salt stress has a major impact on agricultural land worldwide. Poor irrigation and the unregulated use of fertilizers have resulted in the accumulation of salt in the soil. The use of nanofillers is a promising technique that can alleviate the adverse effect of abiotic stresses. In this study, the effect of calcium phosphate nanoparticles (CaP-NPs) was evaluated on coriander plants grown under salt stress. For salt stress application, 100 and 150 mM NaCl solutions were used along with a control group (water only; EC: 0.6 dS m^-1). Meanwhile, a 50 mg L^-1 CaP-NPs solution was applied as a foliar spray. Salt stress specifically at 150 mM greatly reduced the growth, biomass, physiological, and biochemical attributes of coriander plants. In contrast, CaP-NPs effectively ameliorated oxidative stress caused by salt stress, enhancing growth, biomass, physiological and biochemical attributes. Besides this, foliar spray of CaP-NPs at 50 mg L^-1 modulated the enzymatic antioxidant defense system. Salt stress also disturbed ionic balance, as it increased the Na⁺ concentration in the roots and shoots of coriander plants. Salt stress reduced the K⁺/Na⁺ ratio and disturbed ion regulation. On the other hand, the CaP-NPs application increased K⁺ uptake and maintained the K⁺/Na⁺ ratio. Overall, the CaP-NPs application was effective in alleviating salt stress in coriander plants. The use of CaP-NPs in agriculture can do a dual job, as it can alleviate the toxic effect of salt stress and also improve the nutrient use efficiency of plants.