Ambient UV-B radiation inhibits the growth and physiology of Brassica napus L. on the Qinghai-Tibetan plateau

Increased amounts of ultraviolet-B (UV-B) radiation reaching the Earth's surface through stratospheric ozone depletion are expected to have a negative effect on plant responses. However, the reliability of extrapolating indoor experiments to infer plant responses under field conditions has been questioned. Here, we report the growth and physiological responses of Brassica napus L. crops grown on the Qinghai-Tibetan plateau to different levels of ambient UV-B radiation (100%, 70%, and 25%). Here, we aimed to obtain a realistic evaluation of the effect of high UV-B radiation on B. napus L. crops in this region. We used three experimental groups: control (ambient UV-B radiation), T1 (25% exclusion of solar UV-B), and T2 (70% exclusion of solar UV-B). Compared to the control, exclusion of solar UV-B radiation enhanced specific leaf weight (SLW) and caused plant height increased with a significant increase in biomass. Ambient UV-B radiation caused the UV-B absorbing compounds of the leaves to increase, while chlorophyll a, b, and (a + b) content decreased. No significant differences in carotenoid content were detected among the three groups. Compared to the control, exclusion of solar UV-B radiation reduced antioxidant enzyme activity. Moreover, the results showed that exposure to UV-B radiation caused B. napus to (i) increase UV-B absorbing compounds to reduce the transmittance of UV photons through the leaf tissue, (ii) enhance antioxidant enzyme activity to scavenge reactive oxygen species (ROS), and (iii) increase carotenoids to prevent oxidative damage. However, the bleaching of chlorophyll a and damage to the photosynthetic apparatus by solar UV-B radiation caused a reduction in the photosynthetic rate.