[Effects of short-term enhanced UV-B radiation on the PS II photochemical efficiency of alpine plant Saussurea superba].

A simulation experiment of short term supplementation of UV-B was conducted to study the changes of chlorophyll fluorescence coefficients of alpine plant Saussurea superba under three typical weather conditions(sunny,cloudy,and shady) in Qinghai-Tibet Plateau.When the weather changed from sunny to shady,the maximal quantum efficiency of PS Ⅱ photochemistry(Fv/Fm) after 3 minutes of dark adaptation increased significantly,the actual photochemical efficiency of PSⅡ(ΦPSⅡ) and photochemical quenching(qP) also increased,but the non-photochemical quenching(NPQ) decreased,demonstrating that PAR was the main factor affecting the PSⅡ photochemical efficiency of S.superba.After the short term supplementation of UV-B,the Fv/Fm and NPQ under the three typical weather conditions had a slight decrease but the ΦPSⅡ and qP had a slight increase,while the photosynthetic gas exchange had less change.The increasing trend of net photosynthetic rate Pn and ΦPSⅡ under enhanced UV-B radiation could be related to the existence of more UV-A component,and also,benefited from the increased leaf thickness.UV-B radiation had potential negative effects on leaf photosynthetic components.