Responses of PSII photochemistry efficiency and photosynthetic pigments of Saussurea superba to short-term UV-B-supplementation
高山植物美丽风毛菊PSII光化学效率和光合色素对短期增补UV-B辐射的响应

Aims Native alpine plants that have grown and evolved on the Qinghai-Tibetan Plateau of China for a long time have developed a strong adaptation capacity for harsh environmental factors,such as low temperature,low air pressure,strong sunlight and solar UV-B radiation.The objective of this study was to determine the response of PSII photochemistry efficiency to short-term enhanced solar UV-B intensity in alpine plants.We examined whether UV-B-absorbing compounds were sufficiently efficient to protect the photosynthetic apparatus from UV-B photo-inactivation or photo-damage and evaluated the influence of UV-B radiation on photosynthetic pigments.Methods Field experiments were conducted during the 2008 and 2009 growing seasons in alpine Kobresia humilis meadow near Haibei Alpine Meadow Ecosystem Research Station(37°29’-37°45’ N,101°12’-101°33’ E;alt.3 200 m) using the native alpine plant Saussurea superba.Short-term UV-B-supplementation studies were performed over 5 days using UV-B-313 fluorescence lamps,which were filtered with a cellulose diacetate film to get increased UV-B treatment and a Mylar film as a control.Pulse-modulated in-vivo chlorophyll fluorescence was used to obtain rapid information of UV-B on photosynthetic processes.The 3-min dark-adapted maximum quantum efficiency of PSII photochemistry,F(v)/F(m),and PSII photochemistry efficiency were measured under natural sunlight.The contents of photosynthetic pigments and UV-B-absorbing compounds were analyzed based on leaf area unit.Important findings Although there was no significant difference,F(v)/F(m) showed a decreasing trend after short-term exposure to enhanced UV-B radiation in all measurements throughout the growing season.The reduction of the actual photochemical quantum efficiency and photochemical quenching as well as the increase of non-photochemical quenching in UV-B supplemented treatment,when compared to the control,indicated therewas a decrease in PSII photochemistry efficiency and an increase in non-photochemical quenching.These phenomena indicated photo-inactivation or photo-damage of photosynthesis occurred in the PSII reaction center.The photosynthetic pigments showed a small decrease in the UV-B supplemented treatment,which may be related to the enhancement of photo-oxidation,a reduction of pigment synthesis and small variation of leaf thickness.The UV-B-absorbing compounds were not influenced by short-term enhancement of UV-B radiation when analyzed based on leaf area unit.This demonstrated that higher contents of UV-B-absorbing compounds in the epidermal layer of alpine plant S.superba were efficient for defense against UV-B radiation and stabilized for further enhancement of UV-B radiation