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 propose that some substance which have calcium (Ca) as its principal component could be a retardant, atmospheric F contamination to vegetation and the role of the application of foliar Ca are scantly reported. This study deals with F exposure approaches of roots and leaves of pakchoi, together with the foliar application of Ca(NO 3 ) 2 , and analyses some biochemical parameters to evaluate F toxicity under both exposure and the remedial effects of foliar Ca. The results showed that F concentration of pakchoi leaves (LF) was correlated with exogenous F level positively in both foliar and root exposure series, and F concentration of pakchoi roots (RF) was only changed under root exposure treatments. Ca supplement (0.5, 1 g/L) significantly decreased plant F concentration. Both exposure treatments caused lipid peroxidation in plants and exogenous Ca alleviated the toxity of Fto 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 impaire pakchoi growth and disturb photosynthesis, and foliar Ca showed a retarder effect to F toxicity of plants through alleviating chlorophyll decomposition, increasing protein content and alleviating oxidative damage.