Combined effects of elevated O3 concentration and UV-B radiation on photosynthetic characteristics of soybean
地表臭氧浓度增加和UV-B辐射增强及其复合处理对大豆光合特性的影响

During the last several decades, significant reductions in the concentrations of stratospheric ozone(O3) have been reported. This reduced ozone concentration causes an increment in ultraviolet-B radiation approaching to the surface earth. The elevated UV-B radiation and increased tropospheric O3 concentrations maybe occur together and cause reductions in physiological and biochemical characteristics of crops and economic plants. The effects of UV-B and O3 on plant growth and productivity have been reported separately for a large number of species by filed experiment, but only few experiments have focused on their interaction, it is not clear whether UV-B and O3 induced damages are brought about with similar mechanisms. This uncertainty has largely been due to the lack of an experimental approachs to investigate the responses of a single species exposed to UV-B and O3 under well-defined experimental conditions. Studies were conducted under the open-top-chambers conditions so as to assess photosynthesis changes of soybean (Glycine max, Bayuehuang) with supplemental UV-B radiation (10%-10.9% higher than control group, T1) and enhanced ozone , separately and in combination (combination treatment, T3), by investigating photosynthetic pigment, flavonoid content and gas exchange parameters with application of LCpro+ Portable Photosynthesis System. Results indicate that net photosynthetic rate(Pn),maximum photosynthetic rate(Pmax), somatic conductance(Gs), half-saturation light intensity(Ik)and stomatal limitation (Ls)of T1 treatment decreased significantly compared with CK (control group, natural air and UV-B radiant intensity condition). With same references, inter-cellular CO2 concentration(Ci)and flavonoid content increased, the apparent quantum yield(AQY) and the dark respiration rate (Rd)raised first and then decreased, and the cartenoid content decreased first and then raised while the content of chlorophyll had faint decrease if compared with CK. The change pattern of Pn, Pmax, Ik, Gs, Ci and Ls of T2 treatment was similar to those of T1 treatment while the content of chlorophyll and cartenoid decreased significantly compared with CK; flavonoid content of T2 showed slightly decrease at early stages, but sharp increase at latter stages. The change pattern of Pn, Pmax, Ik, Gs, Ls, Ci and Rd of T3 treatment was also similar to those of T1 treatment while the content of cartenoid and chlorophyll decreased obviously compared with CK with lower chlorophyll content than that of T1 and T2. Obviously, enhanced ozone caused significant decrease in chlorophyll content, but supplemental UV-B radiation had no impressive effect on it. Compared with UV-B and O3 alone, UV-B and O3 in combination enhanced the negative effects on soybean chlorophyll content, and ozone stress dominated the combination stress effect of O3 and UV-B. The decrease of photosynthesis was mainly due to non-stomatal factors. UV-B and O3 in combination enhanced the negative effects on soybe