小冠开心形和细型主干形‘玉露香’梨光能截获与光合作用差异

Effect of Tree-shape of ‘Yuluxiang’ Pear on Light Energy Interception and Photosynthetic Characteristics

小冠开心形和细型主干形是黄土高原梨树生产中的主要树形模式。为阐述这两种树形对冠层光能截获和叶片光合功能的影响,以山西芮城县4年生的‘玉露香’梨为试材,2017年和2018年连续两年测定了冠层截获的光合有效辐射PAR、叶片光合的光响应特性、荧光淬灭动力学特性以及光午休期间叶片的热耗散特性和光呼吸。结果表明:小冠开心形冠层不同方位和不同时刻截获的PAR均高于细型主干形,平均提高47.6%;与细型主干形相比,小冠开心形叶片光响应的最大净光合速率Pnmax,p与光饱和点LSP显著升高;光合碳同化过程的3个限制因子中,磷酸丙糖利用速率Vtpu对冠层光环境变化最敏感。正午强光胁迫下,小冠开心形叶片光呼吸速率Pr与总光合速率Pg的比例(Pr/Pg)比细型主干形叶片提高58.5%,NPQ中可恢复组分r(qE)提高了8.9%,而不可恢复组分r(qI)降低了75.0%。两种树形相比,小冠开心形梨树冠层可截获更多的光能,叶片的光合能力更强,强光胁迫时能够通过更高效的热耗散和光呼吸进行自我保护,可作为黄土高原产区梨树适宜树形。

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.