Abstract: 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 PSⅡ photochemistry (F_v/F_m) after 3 minutes of dark adaptation increased significantly, the actual photochemical efficiency of PSⅡ (Φ_PSⅡ) and photochemical quenching (q_P) 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 F_v/F_m and NPQ under the three typical weather conditions had a slight decrease but the Φ_PSⅡ and q_P had a slight increase, while the photosynthetic gas exchange had less change. The increasing trend of net photosynthetic rate P_n and Φ_PSⅡ 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.

Key words: Saussurea superb, chlorophyll fluorescence, PSⅡ photochemical efficiency, Qinghai-Tibet Plateau, UV-B radiation, weather