Characteristics of seasonal and altitude variation of UV-absorbing compounds content in three alpine plants on Qinghai-Tibet plateau.

The content variation of UV-absorbing compounds in Kobresia humilis,Polygonum viviparum and Plantago depressa was studied in growing season at different altitudes in order to insight into their adaptation mechanism to extreme environment at alpine region.The results showed that UV-absorbing compounds content in the leaves of P.viviparum was the highest,K.humilis took the second place,while that was the lowest in P.depressa in the growing season.As the altitudes elevating,the content of UV-absorbing compounds inclined to increase in the three alpine plants and which had the closely positive relationship with the elevation.Seasonal variation of UV-absorbing compounds content in three species appeared only monotonic curve in growing season.However,it showed some differences in three alpine plants.The UV-absorbing compounds content had the highest value at the beginning of the exuberance(in June) in K.humilis and P.viviparum,then it began decreased after that period.Seasonal fluctuation of UV-absorbing compounds in the two species had some positive relationship with the UV-B radiation intensity.While which seemed to fluctuate with its developmental process in P.depressa.It had the highest value in the middle of the exuberance(in July) at different altitudes and inclined to decrease in withering period.The seasonal variation of UV-absorbing compounds content had some negative relationship with the UV-B radiation intensity.Therefore,the differences of seasonal and altitudes variation of UV-absorbing componds among three alpine plants were probably related with the genetics characteristics and adaptation to extremly high UV-B radiation stress in alpine region.