中文摘要：

在大田管理条件下，以不打顶为对照，研究了打顶对芝麻不同叶位叶片光合特性的影响。结果表明：芝麻叶片在打顶后通过调节合适的气孔开度来控制对蒸腾强度的调节，使气体交换达到一个经济合理的阈值，从而提高光能利用效率（LUE）和水分利用效率（WUE）。打顶使芝麻各部位叶片蒸腾强度（Tr）和气孔导度（Gs）都同时下降，平均比不打顶的分别下降4．71％和8．81％，而光合速率和水分利用效率分别比不打顶的高出5．97％和13．96％。打顶与不打顶各叶位间比较，上、中、下三叶位叶片光合速率（Pn）、叶片光能利用效率、叶片水分利用效率、蒸腾强度和气孔导度都达极显著水平。打顶后，在生育后期中、下部叶位叶片仍具有较高的光合效率、光能利用效率与水分利用效率。

英文摘要：

The experiment was carried out under field condition to investigate the effect of topping on photosynthetic characteristics of sesame leaves at different position. The results indicated that leaves controlled transpiration rate by regulating the stomatal aperture, so that gas exchange reached a threshold of economic rationality and improved light energy use efficiency （LUE） and water use efficiency （WUE） after topping. Transpiration rate and stomatal conductance decreased in different leaves by 4.71% and 8.81% respectively after topping, whereas photosynthetic rates and water use efficiency increased by 5.97% and 13.96% respectively. There were significant differences in photosynthetic rate （ Pn）, LUE, WUE, transpiration rate （Tr） and stomatal conductance （Gs） of upper leaves, middle leaves and lower leaves between topping and control treatment. Middle leaves and lower leaves had higher photosynthetic rates, light energy utilization efficiency and water use efficiency than no topping in late stage.