Foliar Application of Ca in Alleviation of Atmospheric Fluoride Stress on Leafy Vegetable and Reduction of Potential Dietary Health Risk

While the macronutrient calcium (Ca) has been utilized to mitigate fluorine (F) toxicity in soils for plants, its role in alleviating phytotoxicity from atmospheric F exposure remains underexplored. This study investigates the effect of foliar-applied Ca on the growth, physio-biochemical characteristics, and F accumulation in Chinese cabbage (Brassica chinensis L.) following both foliar and root F exposure. Results show that foliar application of Ca (0.5 and 1.0 g L⁻¹) significantly enhanced the root length, plant height, and biomass of plants exposed to foliar F at 20 mg L⁻¹, in comparison to the control group, with no notable improvement observed in plants subjected to root F exposure. Foliar application of Ca at 0.5 g L⁻¹ increased chlorophyll production, alleviated the oxidative impairment in leaves, and mediated protective responses specifically under atmospheric F stress, as evidenced by increased chlorophyll concentration and reduced MDA and proline levels. In seedlings with foliar F exposure, F concentration in leaves decreased by 19.9% following foliar application of 1.0 g L⁻¹ Ca compared to the control group without Ca. Additionally, foliar application of Ca at 1.0 g L⁻¹ showed potential in mitigating the health risks associated with consumption of the leafy vegetable grown in F-enriched atmospheres. These findings suggest that foliar Ca application is a promising strategy for mitigating the adverse effects of atmospheric F on leafy vegetables.