Abstract: Taking the main companion species Saussurea superba in an alpine Kobresia humilis meadow on Qinghai-Tibet Plateau as test material, a UV-B
exclusion experiment with UV-B excluding and UV-B transmitting filters was performed to study the effects of strong solar UV-B on the photosynthesis, photosynthetic pigments, and UV-B-absorbing compounds of S. superba, aimed to examine the adaptation capability of alpine plants to strong solar UV-B radiation. The removal of UV-B components from natural sunlight increased the net photosynthetic rate (P<0.05) and PSⅡ photochemistry efficiency of S. superba. The relatively increased leaf thickness under ambient UV-B could compensate the photo-oxidation of photosynthetic pigments, an inherent characteristic of alpine plants growing in intense UV-B. Short-term removal of UV-B radiation had no obvious effects on the UV-B absorbing compounds, suggesting that these compounds in epidermal layer of S. superba could hardly be affected by the environment. It was concluded that the increase of photosynthetic pigment contents due to the enhancement of leaf thickness was a specious phenomenon, but the strong solar UV-B radiation on Qinghai-Tibet Plateau still had a potential negative impact on the photo-physiological processes in alpine plant S. superba.

Key words: alpine plant, photosynthesis, PSⅡ photochemistry efficiency, Qinghai-Tibet Plateau, UV-B-absorbing compounds, UV-B radiation, soybean, intercropping, lodging resistance, cellulose, sugar, enzyme activity.