Effect of exogenous Ca on the physiology and growth indicators of pakchoi under foliar and root fluorine stress

Fluorine (F) is not an essential element for vegetation and excessive F can be phytotoxic to plant growth, which can cause fluorosis to human beings by ingesting F-contaminated plant. Although there have been some studies focusing on the toxicity of F to plants and the retarding effect of Ca to F-stress plant, atmospheric F contamination to vegetation and the role of the application of foliar Ca are scantly reported. This study investigated several biochemical parameters to evaluate F toxicity under both F-exposure (root and leaf F-exposure) and the remedial effects of foliar Ca. The results showed that F concentration of pakchoi leaves was correlated with exogenous F level positively in both foliar and root F-exposure series, and F concentration of pakchoi roots was only changed under root F-exposure treatments. Ca supplement (0.5 g/L and 1 g/L) significantly decreased plant F concentration. Both F-exposure treatments caused lipid peroxidation in plants and exogenous Ca alleviated the toxicity of F to pakchoi. Meanwhile, chlorophyll-a concentration was decreased by foliar and root F, whereas chlorophyll-b concentration was only affected by foliar F, and chlorophyll-a concentration could be elevated by exogenous Ca but chlorophyll-b could not. It was concluded that both atmospheric and root F can impair pakchoi growth and disturb photosynthesis, and foliar Ca showed an ameliorative effect to F toxicity of pakchoi through alleviating chlorophyll decomposition, increasing protein content and alleviating oxidative damage.