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

Responses of PSII photochemistry efficiency and photosynthetic pigments of Saussurea superba to short-term UV-B-supplementation

在中国科学院海北高寒草甸生态系统实验站的综合观测场,于植物生长季的不同月份进行短期增补UV-B辐射的模拟试验,研究了高山植物美丽风毛菊(Saussurea superba)的PSII光化学效率、光合色素和UV-B吸收物质对增强UV-B辐射的响应。结果表明,尽管差异不显著,暗适应3min的PSII最大光化学量子效率在不同月份均有降低的趋势,说明增强UV-B辐射能加剧光合机构的光抑制。不同月份短期增补UV-B辐射均引起光下PSII实际光化学量子效率和光化学猝灭系数的降低,以及非光化学猝灭系数的增高,表明增强UV-B辐射能降低叶片的光能捕获效率,促进非光化学能量耗散过程。增补UV-B辐射后,叶片光合色素的含量略有降低趋势,可能与短时间内光合色素形成过程受抑制和光氧化程度的加剧,以及叶片厚度的略微降低有关。UV-B吸收物质的含量在不同月份没有一致和较为显著的变化,说明高原强UV-B环境下生存的美丽风毛菊叶表皮层中由类黄酮和衍生多酚类组成的内部紫外屏蔽物质相对稳定,倾向于较少受增补UV-B辐射的影响。

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