Characteristics of Mango Leaf Photosynthetic Inhibition by Enhanced UV-B Radiation

To investigate the photosynthetic change characteristics of mango leaves under enhanced UV-B radiation, adult 'Tainong No. 1' mango (Mangifera indica) trees were treated (N = nine individuals) with simulated enhanced UV-B radiation [24 and 96 kJ/(m(2)center dot d)] in the field, and the photochemical reactions, activities of key enzymes in carbon assimilation, and the expression of genes were observed. The results showed that compared with the control, there was a decrease in tree yield, soluble sugar, sugar-acid ratio, and vitamin C of the fruits under the 96 kJ/(m(2)center dot d) treatment, while no significant changes were observed under 24 kJ/(m(2)center dot d). After 20 or 40 days, the leaves' net photosynthetic rate (Pn), stomatal conductance (Sc), transpiration rate (Tr), intercellular CO2 concentration (Ci), and chlorophyll a/b under exposure to 96 kJ/(m(2)center dot d) of UV-B were significantly lower than in the control, whereas chlorophyll a, chlorophyll b, carotenoids, Hill reaction activity, photochemical quenching coefficient (qP), and Rubisco activities were significantly higher. In contrast, the Hill activity and Rubisco activity under 24 kJ/(m(2)center dot d) were significantly higher than the control, and increased by 350% and 30.8%, respectively, while Pn, Sc, Tr, Ci, and the content of photosynthetic pigments were similar to the control. The expression of gene coding the Rubisco big subunit (rbcL) was inhibited by the 96 kJ/(m(2)center dot d) treatment. We conclude that stomatal limitation was directly induced by 96 kJ/(m(2)center dot d), resulting in the inhibition of photosynthesis and the reduction in yield and deterioration of the quality of mango.

Automated summary

The study found that under 96 kJ/(m²·d) of UV-B radiation, mango trees showed decreased yield, decreased sugar content and vitamin C in fruits, and inhibited photosynthesis in leaves; while under 24 kJ/(m²·d), the content of photosynthetic pigments in leaves increased, but overall performance was similar to the control group.