Effect of enhanced UV-B radiation on photosynthesis and photosynthetic pigments in alpine plants Saussurea superba.

Strong solar UV-B radiation is the main environmental stress factors in Qinghai-Tibet region.A UV-B-supplementation study was performed in alpine Kobresia humilis meadow using cellulose diacetate filtered fluorescence UV-B lamps,comparing to the control lamps with a Mylar film in order to remove UV-B emission.Results from alpine plant Saussurea superba indicated that net photosynthetic rate,Pn,was enhanced after supplementing solar UV-B intensity,resulting from the opening of stomatal conductance.However,ΦPSⅡ showed a decrease after 11 and 16 days of treatment,suggesting that accumulation of damage from UV-B radiation could reduce PSⅡ photochemistry efficiency.Although there was an increase of photosynthetic pigments within the first 10 days of treatment,they decreased by the end of experiment indicating that UV-B radiation causes photo-damage of photosynthetic pigments and that the initial increase of its contents was mainly due to the increase of leaf thickness.UV-B-absorbing compounds were not altered after enhancement of UV-B radiation suggesting that there were higher levels of flavonoid compounds in the epidermal layer of S.superba acting to protect photosynthetic function from UV-B damage.In summary,the short-term enhanced UV-B radiation was beneficial for Gs and photosynthetic pigments,but there were still negative effects on photosynthesis function of this native alpine plant.