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

基于开顶式气室(OTC),系统开展了地表O3增加和UV-B增强及其复合处理下(自然空气,CK;10%UV-B增强,T1;100nmol/mol O3,T2;100 nmol/mol O3+10%UV-B增强,T3)大豆光合气体交换、光响应、光合色素和类黄酮含量等参数的观测与分析研究。结果表明,与对照相比,T1和T2单因子处理组的如下指标有相似变化:气孔导度、气孔限制值下降,胞间二氧化碳浓度上升,净光合速率、最大净光合速率、半饱和光强显著降低,表观量子效率和暗呼吸速率先升后降。T1的叶绿素含量降低不显著,类胡萝卜素含量先降后升,类黄酮含量上升,而T2的叶绿素和类胡萝卜素含量显著降低,类黄酮含量先降后升。复合处理下,与CK相比各指标的变化和单因子相似,影响程度均强于两单因子组。因此,100 nmol/mol O3浓度增加和10%UV-B辐射增强复合处理对大豆叶绿素含量的影响存在协同作用,且O3胁迫起了主导作用。光合作用下降的主要原因均是非气孔因素,复合处理对大豆光合作用的影响比两因子单独胁迫有所加深,是O3和UV-B共同作用的结果。

Combined effects of elevated O3 concentration and UV-B radiation on photosynthetic characteristics of soybean

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(P_n),maximum photosynthetic rate(P_max), somatic conductance(G_s), half-saturation light intensity(I_k)and stomatal limitation (L_s)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(C_i)and flavonoid content increased, the apparent quantum yield(AQY) and the dark respiration rate (R_d)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 P_n, P_max, I_k, G_s, C_i and L_s 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 P_n, P_max, I_k, G_s, L_s, C_i and R_d 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 soybean compared with UV-B and O₃ alone.