CO_2倍增及UV-B增强对大豆植株生长和根际微生物的影响

Effects of Doubled Carbon Dioxide and Enhanced UV-B Radiation on Growth and Rhizosphere Microorganisms in Soybean(Glycine max Merr.)

以大豆‘齐黄27’为研究材料，采用人工气候室模拟大气CO2浓度倍增（350～700μmol·mol^-1）及紫外线B（UV—B，280～320nm）辐射增强（4～15μw·cm^-2）的环境条件，研究了CO2浓度增加及UV—B辐射增强对大豆生育前期的生长及根瘤、根际微生物数量的影响。结果表明：（1）增强UV—B能显著减少大豆植株地上部生物量，而对株高的抑制作用不显著；CO2浓度倍增促使大豆株高和地上生物量显著增加，对根系生物量的促进作用不显著，但能够减轻UV—B辐射增强对地上及根系生物量的抑制作用；CO2浓度增加、UV—B辐射增强及其复合胁迫均导致大豆植株根冠比下降，且复合胁迫对根冠比的抑制作用更明显。（2）CO2浓度倍增降低了大豆叶片叶绿素、类胡萝卜素及花青素含量，提高了净光合速率；UV-B辐射增强导致叶绿素含量减少，光合速率下降，却增加了类胡萝卜素及花青素含量；CO2浓度增加、UV-B辐射增强复合处理对叶片色素含量及光合速率的影响具有复合效应。（3）CO2浓度倍增能够促进根瘤数量及根际真菌数量的增加，而UV-B增强处理则显著降低细菌和放线菌的数量；CO2浓度倍增能够缓解UV-B增强处理对放线菌的抑制作用，却导致根际细菌数量进一步减少。研究发现，CO2浓度增加及UV—B辐射增强对大豆生育前期植株生长、叶片色素含量及根际微生物数量存在抑制或促进效应，而且在某些性状上存在复合效应，它们可能主要是通过调节大豆植株的干物质分配及根系的代谢间接影响根瘤数量及根际微生物数量。

The effects of doubled carbon dioxide concentration（350～700μmol · mol^-1） and enhanced UV-B radiation （4～15μW · cm^-2） on soybean growth and rhizosphere microorganisms were imitated in artificial climate room. The soybean variety was Qihuang 27. The results showed that： （1）Doubled CO2 significantly increased the seedlings height and overground biomass. It also improved the underground biomass but not reach to a significant different level. Enhanced UV-B radiation significantly decreased overground biomass. However,it had not significant effects on seedlings height. When the two factors combined, doubled CO2 could alleviated the opposite effects induced by enhanced UV-B. Root/shoot ratio was all significantly decreased by doubled CO2, enhanced UV-B and their combination, while a more pronounced decrease occurred when the two stresses were applied together. （2）Doubled CO2 significantly decreased the contents of chlorophyll,carotenoid and anthocyanin, and significantly increased photosynthesis. Enhanced UV-B radiation induced significantly decreases in chlorophyll content and photosynthesis, and significantly increase in contents of carotenoid and anthocyanin. When two stresses were supplied together, the additive effects were observed in pigment contents and photosynthesis. （3）In relation to the number of root nodule,bacteria and epiphyte,doubled CO2 significantly increased the number of root nodule and epiphyte. However, enhanced UV-B significantly decreased the number of bacteria and epiphyte. In combination of doubled CO2 and enhanced UV-B,the effects of doubled CO2 could alleviated the inhibition of enhanced UV-B on the number of epiphyte,but it exaggerated the decrease on the number of bacteria induced by enhanced UV-B. In conclusion,doubled CO2 and enhanced UV-B maybe indirectly affect the number of root nodule and rhizosphere microorganisms through the effects on dry mass distributions and root metabolism.