夏季遮阳对‘红阳’猕猴桃净光合速率的影响及其与生理生态因子的关系

Impact of summer shading on net photosynthetic rate of Actinidia chinensis 'Hongyang' and its related eco-physiological factors

【目的】探明夏季遮阳对‘红阳’猕猴桃叶片光合特性的影响。【方法】设置0%、35%和70%3种遮阳处理,利用CI-340(CID Inc.,USA)便携式光合仪测量‘红阳’猕猴桃的气体交换参数,分析‘红阳’猕猴桃净光合速率(P_n)的日变化规律及其与生理生态因子之间的关系。【结果】夏季‘红阳’猕猴桃叶片Pn日变化在0%和35%遮阳处理下为典型的"双峰"曲线,在70%遮阳处理下为单峰曲线;35%遮阳处理下‘红阳’猕猴桃P_n日最高值为14.715μmol·m^(-2)·s^(-1),日均值为7.889μmol·m^(-2)·s^(-1),明显高于0%和70%遮阳处理组。【结论】在夏季,适度遮阳可有效地提高‘红阳’猕猴桃叶片的P_n。但早晨和傍晚遮阳并不利于‘红阳’猕猴桃叶片进行光合作用。光合有效辐射和叶面温度是‘红阳’猕猴桃净光合速率(P_n)的主要限制因子,而蒸腾速率是主要决定因子。

[ Objective] The study explored the diurnal changes in photosynthetic parameters of Actinidia chinemis ‘Hongyang＇ under different shading treatments in summer. [Methods] 0% （control）, 35% and 70% shading levels were used in this study, and the treatments began on June 10, 2015. Gas exchange characteristics of the plants were detected on sunny days （July 13 to14 and August 3 to 4, 2015） from 6：00 to 18：00 at 1.5 h intervals. Photosynthesis related parameters including P., transpiration rate （Tr）, stomatal conductance （Gs）, intercellular CO2 concentration （Ci）, leaf temperature （Tleaf） and environmental factors including photosynthetic active radiation （PAR）, air temperature （ta）, air CO2 concentration （Ca）, and air relative humidity （RH） were automatically measured and recorded with a portable photosynthesis system with an air flow rate of 0.3 L. min- 1 and an open system （CI-340, CID Inc., USA）. Central portion of each leaf was used for photosynthesis measurement to ensure sample uniformity. Measurements were replicated 6 times （n = 6） for each treatment. [Results] （1） A typical double-peak pattern of diurnal changes in P, with an obvious midday depression was recorded in the control and the 35% shading treatment. The value of the first peak of Po occurred at 9：00 and was the highest. In the control and under 35% shading treatment, this peak value was 11.198 and 14.715μmol, m-2. s-a, respectively, and the value of the second peak occurring at 15：00 was 7.817 and 8.980 μmol. m-2. s-1, respectively. In contrast, a single-peak diurnal curve of P. was found in the 70% shading treatment, the peak value of which was 10.982 μmol. m-2. s-1appearing at 9：00. The daily average value of Pn was 7.889, 6.058, and 3.921 μmol. m-2. s-1 in the 35% shading treatment, the control and the 70% shading treatment, respectively. However, the value of PN was signifi- cantly higher in the control than in the 35% and 70% shading treatments at 6：00 and 18：00. （2） The 94.8% and 99.3% of the variations in P. could be separately explained by 6 eco-physiological factors, such as PAR, Ca, Tr, G, Ci, and Tleaf in the control and the 35% shading treatments, respectively. 97.3% of the variation in Pn could be explained by Ca, RH, Gs and Ci under 70% shading treatment. Further, signifi- cant negative effects of PAR, Ci, and Tleaf but significant positive effects of C, Tr, and G, on Po were found in the control and under the 35% shading treatment. As for the 70% shading treatment, negative factors and the direct positive factors were Ci, RH and Ca, G, respectively. According to the decision coefficient, PAR, Gs, Ci and Tleaf were the four inhibitors and Ca and Tr were the 2 determinants which affected the Pn of A. chinensis ＇ Hongyang＇ in the control. The inhibitors and the determinants were PAR, Tleof and Tr, Gr and Cs under the 35% shading treatment, respectively, and were Ci, RH and Ca, Gs under the 70% shading treatment, respectively. [Conclusion] In summer, there was an obvious midday depression of P. in A. chifecting the Pn ofA. ‘chinensis ＇ ‘Hongyang＇, while Tr was its main determinant. We suggest that, for the cultivation of the A. chinensis ‘Hongyang＇, it is better to select an open region with a good air circulation, such as flat terrain or less slope gradient and southern side of hills, and to use moderate shading treatment in day time but avoiding shading in the early morning and at dusk during summer.