Short-term effects of experimental warming and enhanced ultraviolet-B radiation on photosynthesis and antioxidant defense of Picea asperata seedlings

Picea asperata is a dominant tree species in the southeast of the Tibetan Plateau of China. This paper studies the short-term effects of warming, enhanced UV-B (290-315 nm) and their combination on growth, photosynthesis and antioxidant defense system (AOS) of P. asperata seedlings. The experimental design included two levels of UV-B (ambient UV-B and enhanced by 30% UV-B) and two levels of temperature (ambient temperature and warmed temperature by 1.74A degrees C). Although enhanced UV-B increased the efficiency of antioxidant defense system (AOS) including UV-B absorbing compounds, carotenoids, and antioxidant enzymes such as superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT) and peroxidase (POD), it induced over production of reactive oxygen species (ROS) and oxidative stress eventually. Moreover, enhanced UV-B reduced growth, chlorophyll content and net photosynthetic rate (A). Warming did not significantly affect dry mass accumulation of P. asperata seedlings while it accelerated stem elongation and stimulated A. Furthermore, warming alleviated the harmful effects of enhanced UV-B on the growth and photosynthesis. It also increased the antioxidant capacities of seedlings exposed to enhanced UV-B. Our results showed that the growth of P. asperata seedlings was inhibited by a combination of enhanced UV-B and warming, however, to some extent warming alleviated UV-B effects.