Stomatal and nonstomatal limitations of photosynthesis in P. radiatus L. seedling leaves under the combination of enhanced UV-B radiation and Cd2+_stress_ _ | 增强UV-B辐射和Cd2+_复合胁迫下绿豆幼苗Cd积累和光合作用的气孔和非气孔限制_

Chinese. ［目的］研究增强UV-B辐射和Cd2+_复合胁迫下绿豆（Phaseolus radiatus_L.）幼苗Cd积累和光合作用的气孔和非气孔限制因素。［方法］试验设1个对照（CK）和3个试验组，分别为增强UV-B辐射（UV-B）组、Cd2+（Cd）组、增强UV-B辐射＋Cd2+（UV-B＋Cd）组，研究0.35 W/m2的UV-B辐射、1 μmol/L Cd2+_及其复合胁迫下绿豆幼苗对Cd的吸收、分配和光合作用的气孔、非气孔限制，分别利用原子吸收分光光度仪和光合测定仪测定Cd在绿豆幼苗各部位的含量及第1对真叶的光合指标。［结果］绿豆幼苗中Cd的积累是根胚轴叶，UV-B对Cd在幼苗中的积累和分配没有影响。此外，各胁迫下幼苗的净光合速率（Pn）、气孔导度（Gs）、光合能力（A0）和羧化效率（dPn/dCi）含量均明显降低。UV-B组的细胞间隙CO2浓度（Ci）升高，气孔限制值（Ls）降低，Pn的降低是非气孔因素。Cd和复合处理组的Ci降低，而Ls升高，Cd组Pn的降低主要是气孔因素。复合组前期以非气孔因素为主，后期主要是气孔因素。［结论］该研究揭示了UV-B辐射和Cd2+_复合胁迫下绿豆幼苗光合变化的主要原因，可为进一步研究提供科学依据。

English. ［Objective］ The research aimed to study the stomatal and nonstomatal limitations of photosynthesis in P. radiatus L. seedling leaves under the combination of enhanced UV-B radiation and Cd2+ stress. ［Method］ The test designed one control group and 3 test groups, enhanced UV-B radiation(UV-B) group, Cd2+ (Cd) group and enhanced UV-B radiation＋Cd2+_(UV-B＋Cd) group respectively. Stomatal and nonstomatal 〖JP3〗limitations of photosynthesis in _P. radiatus_ L. seedling leaves under the combination of 0.35 W/m2 UV-B radiation and 1 μmol/L 〖JP〗Cd2+ stress were studied. Cd concentration in root, hypocotyls, and leaf were determined by atomic absorption spectrometer, respectively. The photosynthetic parameters of the first pair leaves of _P. radiatus_ L. seeding were monitored by TPS-1 photosynthesis system or calculated according to the theory of Farquhar and Sharkey. ［Result］ Cd concentration allocated in different parts of _P. radiatus_ L. was roothypocotylleaf, and UV-B group had no effect on the absorption and allocation in _P. radiatus_ L.. In addition, separated or combined treatments of enhanced UV-B radiation and Cd2+ stress all resulted in a decrease in net photosynthetic rate, stomatal conductance, photosynthetic ability, efficiency of CO2 carboxylation and rubisco content. That intercellular CO2 concentration increased and stomatal limitation value decreased under UV-B treatment indicated that the inhibition of photosynthesis in P. radiatus L. seedling leaves was nonstomatal limitation. That intercellular CO2 concentration decreased and stomatal limitation value increased under Cd treatment and combined treatment showed that the inhibition of photosynthesis in Cd treatment was stomatal limitation and the combined treatment was the results of stomatal and nonstomatal limination. ［Conclusion］The study reveals the main factors of photosynthetic changes of P. radiatus L. seedling under the combination of enhanced UV-B radiation and Cd2+ stress, can provide the scientific basis for deeply research.