Abstract
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/(m2·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/(m2·d) treatment, while no significant changes were observed under 24 kJ/(m2·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/(m2·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/(m2·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/(m2·d) treatment. We conclude that stomatal limitation was directly induced by 96 kJ/(m2·d), resulting in the inhibition of photosynthesis and the reduction in yield and deterioration of the quality of mango.
Highlights
Ultraviolet radiation zone B (UV-B, wavelength 280–320 nm) is largely absorbed by the ozone layer, with only a small amount reaching the ground
Chlorofluorocarbon contamination in the stratosphere has resulted in a decrease in ozone, which in turn has led to an increase in UV-B radiation [1,2], which is referred to as enhanced UV-B radiation
The results showed that both UV-B radiation treatments could improve CO2 fixation by increasing the Ribulose bisphosphate carboxylase oxygenase (Rubisco) activity in the leaves and improving the carbon-fixation reaction
Summary
Ultraviolet radiation zone B (UV-B, wavelength 280–320 nm) is largely absorbed by the ozone layer, with only a small amount reaching the ground. Chlorofluorocarbon contamination in the stratosphere has resulted in a decrease in ozone, which in turn has led to an increase in UV-B radiation [1,2], which is referred to as enhanced UV-B radiation. Without proper control of pollutants, ozone in the stratosphere will continue to decline. It is estimated that the annual increase rate of enhanced UV-B radiation in the Northern. The damage, in turn, has raised concerns about the potential harm of enhanced UV-B radiation. Light is a necessary energy condition for plant photosynthesis, and photosynthetic systems have become targets for enhancing the effects of UV-B radiation stress.
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