【摘要】 【目的】探讨弱光条件下黄瓜(Cucumis sativus)幼苗不同叶位叶片光合特性的响应变化及品种间差异,为日光温室黄瓜冬季生产提供理论依据。【方法】以不耐弱光的‘津研2号’和较耐弱光的‘戴多星’黄瓜幼苗为试材,在人工气候室内用LI-6400光合仪和PAM-2100荧光仪研究弱光[75～85μmol·m-2·s-1,25℃(昼)/18℃(夜)]及常光对照(500～600μmol·m-2·s-1)下黄瓜不同叶位叶片的光合气体交换参数、叶绿素a荧光参数。【结果】弱光处理后,黄瓜第3～5叶净光合速率(Pn)、气孔导度(Gs)、气孔限制值(Ls)、蒸腾速率(Tr)和瞬时水分利用效率(WUE)基本上下降,而胞间CO2浓度(Ci)升高,尤以中部叶变化明显,Pn的下降主要是非气孔因素限制的结果。弱光下第3～5叶光系统Ⅱ(PSⅡ)实际光化学效率(ΦPSⅡ)、光化学反应速率(Prate)、非环式电子传递速率(J)和PSⅡ吸收光能用于光化学反应的比例(P)均下降,光系统间激发能分配不平衡性(β/α-1)增大。弱光下‘津研2号’随叶位的升高其Pn、ΦPSⅡ、J和P等光合、荧光参数基本呈降低趋势,β/α-1有所升高,而‘戴多星’上述参数的变化规律与其对照相似,即中部叶具有较高的光合能力和光化学活性。【结论】弱光抑制了黄瓜幼苗各叶位叶片,尤其降低了中上部叶的光合同化能力和PSⅡ光化学活性。弱光下‘津研2号’幼苗整株持续光合能力明显低于‘戴多星’。更多还原

【Abstract】 【Objective】The aim of this study was to investigate the effects of low light on the photosynthetic characteristics of different position leaves of seedlings in two cucumber (Cucumis sativus L.) varieties and to try to offer some academic base for the cucumber production in solar greenhouse in winter.【Method】Shade-susceptible ‘Jinyan 2’ and shade-tolerant ‘Deltastar’ were planted in the growth chamber. The gas exchange parameters and the chlorophyll a fluorescence parameters of different position leaves in seedlings were measured by the LI-6400 Portable Photosynthesis System and the PAM-2100 Chlorophyll Fluorometer under the low light [75-85 μmol·m-2·s-1, 25℃ (day)/18℃(night)] and control (500-600 μmol·m-2·s-1). 【Result】After treated for 13 days under the low light, the net photosynthesis rate (Pn), stomatal conductance (Gs), stomatal limitation value (Ls), transpiration rate (Tr) and water use efficency (WUE) of different position leaves (from 3rd to 5th) were basically declined and the intercellular CO2 concentration (Ci) was basically increased, especially obvious in middle position leaves in the two cultivars. The principal factorwhich resulted in the decrease of the Pn was the non-stomatal restriction. Under the low light, the photosystem Ⅱ (PSⅡ) actual photochemical efficiency (ΦPSⅡ), the photochemical reaction rate (Prate), the linear whole-chain electron transport rate (J) and the partitioning proportion for photochemical reaction of light energy absorbed by PSⅡ (P) of middle and up position leaves (from 3rd to 5th) of seedlings were declined. At the same time, the imbalance of partitioning of excitation energy between PSⅠ and PSⅡ (β/α-1) was increased. The photochemical reactions of PSⅡ of middle position leaves of seedlings were strongly restrained by the low light. The photosynthetic and fluorescent parameters, such as Pn, ΦPSⅡ, J and P etc., were basically decreased from the bottom to the top leaves in ‘Jinyan 2’ under the low light, but the β/α-1 was increased. Nevertheless, the changing of these parameters just mentioned in ‘Deltastar’ was similar to its control under the low light. Namely, the photosynthetic efficiency and photochemistry activity were stronger in middle position leaves in ‘Deltastar’.【Conclusion】The photosynthetic assimilation and photochemistry activity of PSⅡ of different position leaves are restrained in seedlings of cucumbers under the low light, especially obvious in middle and up position leaves. There are some differences in the effects of low light on photosynthetic characteristics of different position leaves of seedlings in two different tolerance-low-light cucumbers. The capacity of sustaining photosynthesis of whole plant in ‘Jinyan 2’ is weaker than the one in ‘Deltastar’ under the low light.更多还原