半根及半根交替水分胁迫对苹果幼苗光合作用的影响

 【目的】模拟研究定位灌溉及分根区交替灌溉的‘嘎拉’苹果幼苗光合反应，探讨不同水分条件下叶片光合效率的气孔与非气孔限制作用。【方法】采用18% PEG 6000（w/v）模拟水分胁迫，研究了半根（HRS，模拟定位灌溉）、半根交替（AHRS，模拟分根区交替灌溉）及全根水分胁迫（WRS）下苹果光合参数、光合色素、超氧化物歧化酶（SOD）和丙二醛（MDA）含量的变化，及叶绿素荧光反应特点。【结果】水分胁迫条件下叶片光合速率、气孔导度与细胞间隙CO2浓度显著降低，叶温显著升高。HRS叶片MDA含量和SOD活性及叶绿素荧光反应与对照不存在显著差异；AHRS从交替后第2天起，叶片MDA含量显著高于对照，而Fv/Fo与Fv/Fm则显著低于对照；WRS在胁迫第5或6天后，叶绿素与类胡萝卜素含量、Fv/Fo和Fv/Fm、SOD酶活性显著降低，而MDA含量则显著增加。【结论】不同水分胁迫处理光合速率下降的原因存在差异：HRS主要由气孔限制所引起；AHRS既存在气孔限制，也存在非气孔因素限制；而WRS前期由气孔限制引起，随着胁迫时间延长，非气孔限制起着重要作用。

Response of Photosynthesis of Micropropagated Apple Plants to Half Root and Alternate Half Root Water Stress

【Objective】 The response of photosynthesis of apple plants to drought stress which simulated drought stress conditions for roots under localized irrigation and alternate partial rootzone drying. Moreover, stomatal and non-stomatal limitations in photosynthesis under water stress were investigated. 【Method】Water stress was simulated using PEG6000. Compared with good water condition, micropropagated ‘Royal Gala’ apple plants were subjected to half root stress (HRS, to simulate localized irrigation), alternate half root stress (AHRS, to simulate alternate partial rootzone drying), whole root stress (WRS). Their net photosynthesis rate (Pn) and the related photosynthetic parameters, photosynthetic pigment, chlorophyll fluorescence, SOD activity, and malondiadehyde (MDA) content were studied. 【Result and conclusion】Pn, stomatal conductance, substomatal CO2 decreased significantly and leaf temperature increased significantly for all plants under water stress, when compared with CK plants. There were no significant differences of photosynthetic pigment and MDA content, SOD activity and chlorophyll fluorescence response between CK and HRS, indicating that decreased Pn of HRS plants was due to mainly stomatal limitation. Similar foliar photosynthetic pigment and MDA content, SOD activity were found between AHRS and CK while AHRS resulted in higher foliar MDA content and lower Fv/F0 and Fv/Fm than CK from 2nd day after the plants were under water stress. It is suggested that the decreased Pn of AHRS plant should be due both stomatal and non-stomatal limitations. Significantly lower foliar photosynthetic pigment content, SOD activity, Fv/F0 and Fv/Fm, but higher foliar MDA content, were observed on WRS 4 or 5 day after the plants were under drought stress than CK, indicating that the decreased Pn in the first few days after water stress was applied should be due to mainly stomatal limitation, and non stomatal limitation should play an important role thereafter in regulating Pn for WRS plants.