关键词: 梨, 树形, 光能截获, 光合能力, 荧光淬灭动力学, 热耗散, 光呼吸

Abstract: Effect of tree-shape on light energy interception and photosynthetic characteristics were elucidated in the Loess Plateau of China. In this study，four-year-old pears（Pyrus bretschneideri Rehd. ‘Yuluxiang’）of small open-central canopy（SOC）and slender central-leader canopy（SCL）were compared carefully by analyzing light interception，gas exchange and fluorescence quenching. The results demonstrated that PAR values intercepted by SOC at different orientation and different o’clock during the day were higher than SCL（increased by 47.6% on average）. Comparing to SCL，leaf maximum net photosynthetic rate（Pnmax,p）and light saturation point（LSP）of SOC were increased significantly. Among the three limiting factors in process of photosynthetic carbon assimilation，rate of triose-phosphate utilization（Vtpu）was the most sensitive one to the changes of light environment in canopy. Under high light stress，the ratio of photorespiratory rate to gross photosynthetic rate（Pr/Pg）of SOC was increased by 58.5% than that of SCL. Moreover，reversible component in NPQ[r(qE)] was increased by 8.9% while irreversible component in NPQ[r(qE)]was reduced by 75.0% in SOC than that in SCL. In summarize，tree-shape pruning could improve light environment in SOC，which in turn leads to the increased leaf photosynthetic performance and the enhanced photoprotective capacity via more effective thermal dissipation and photorespiration. Therefore，SOC is appropriate tree-shape for pear production in the Loess Plateau of China.

Key words: pear, tree-shape, light energy interception, photosynthetic capacity, fluorescence quenching kinetic, thermal dissipation, photorespiration