Effect of rare earths on plant under supplementary ultraviolet-B radiation: I effect of cerium on growth and photosynthesis in rape seedlings exposed to supplementary ultraviolet-B radiation

Effect of cerium (Ce3+) on growth and photosynthesis in rape seedlings exposed to two levels of ultraviolet-B\ radiation (UV-B, 280 similar to 320 nm) was studied with hydroponics under laboratory conditions. The growth of rape seedlings exposed to two levels of UV-B irradiation (0.15 and 0.35 W(.)m(-2)/T-2) was both heavily restrained. The aboveground growth indices including stem (plant) height, leaf number, leaf area, leaf fresh/dry weight and stem fresh/dry weight were obviously decreased by 13.2% similar to 44.1% (T-1) and 21.4% similar to 49.3% (T-2) . Compared to CK, and except active absorption area Of roots, the belowground indices main root length, root volume and fresh/dry weight by 14.1 % similar to 35.6% (T-1) and 20.3% similar to 42.6% (T-2), respectively. For Ce + UV-B treatments, the aboveground and belowground growth indices were decreased by 4.1% similar to 23.6%, 5.2% similar to 23.3% (Ce + T-1) and 10.8% similar to 28.4%, 7.0% similar to 27.8% (Ce + T-2), lower than those of UV-B treatments mentioned above. These results show that Cc has protective effect on plant against injury of UV-B radiation. Furthermore, the protective effect of Ce on seedlings exposed to T, level of UV-B radiation is superior to T-2 level. Chlorophyll content, net photosynthesis rate, transpiration rate, stomatal conductance and water use efficiency in UV-B treatments decrease dramatically, whereas intercellular CO2 concentration increases. Although these indices in Ce + UV-B treatments decrease compared with those of CK, the decrease in Ce + UV-B treatments are lower than those in UV-B treatment. This phenomenon indicates that the ecophysiological protective effect of Ce is based on improving photosynthesis in plants. The dynamic curves of photosynthesis indices show that the course of light-repair is shortened and the injury to rape seedlings by UV-B radiation stress is alleviated by Ce.