中文摘要：

通过气体交换、荧光猝灭动力学以及反射光谱等技术研究了两个青稞（Hordeum vulgareL.）品种的光合特性及激发能分配。结果表明,青稞的光饱和点1000μmol m^-2s^-1右。在0～500μmol m^-2s^-1光强范围里,青稞叶片的光呼吸（Pr）随着光强升高而增加;光强超过500μmol m^-2s^-1后,光呼吸变化不明显。光呼吸占总光合的比例（Pr/Pm）随光强增强下降。随着光强增强,光系统II开放反应中心转化效率（Fv′/Fm′）,光系统Ⅱ实际光化学量子效率（ΦPSⅡ）,光化学猝灭系数（qP）不断降低而青稞叶片的非光化学猝灭（NPQ）持续升高,说明越来越多的光能以热的形式耗散掉。光谱分析表明△PRI随着青稞叶片暴露于光下的时间迅速增大。因此,光呼吸不是青稞主要的光破坏防御机制,依赖叶黄素循环的热耗散可能是田间青稞耗散过剩光能的主要途径。

英文摘要：

As a local crop of Qinghai-Tibet Plateau, highland barley （Hordeum vulgare L.） has acclimated to the typical habitat with strong light and low O2 to CO2 ratio. Low O2 to CO2 ratio may have a great influence on photorespiration which plays an important role in protecting photosynthetic apparatus against photoinhibition. In this study, we hope to know whether photorespiration plays an important role in photoprotection of highland barley and what are the main photoprotective mechanisms of highland barley. Gas exchange, fluorescence quenching kinetics and reflectance spectrum were investigated to explore the photosynthetic characteristic and allocation of excitated energy in two highland barley cultivars. Results showed that light saturation point of highland barley was about 1 000 μmol m^-2 s^-1. Photorespiration rate （Pr） increased with light intensity increasing while it did not change significantly above 500 μmol m^-2 s^-1. The percentage of photorespiration to total photosynthesis （Pr/Pm） declined gradually with the increase of light intensity. The efficiency of open centers of photosystem II （Fv′/Fm′）, actual photosystem Ⅱ efficiency （Фpsn） and photochemical quenching （qp） all declined with the increase of light intensity; non-photochemical quenching increased with light intensity increasing, indicating that more and more excited energy dissipated as thermal dissipation. Spectrum analysis showed that the change of photochemical reflectance index （△PRI） increased significantly when fully dark-adapted plants were suddenly exposed to light. On these bases, we concluded that photorespiration is not the main pathway for highland barley to relieve strong light stress; thermal dissipation relying on xanthophyll cycle may play an important role in dissipating excessive excited energy in highland barley.