半根及半根交替水分胁迫对苹果幼苗光合作用的影响

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

【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%PEG6000(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。

[Objective] The objective of the present study was to investigate the response of photosynthesis of apple plants to partial and alternate partial root-zone drying, focusing on stomatal and non-stomatal limitations. [Method] 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） and whole root stress （WRS） by regulating the osmotic potential of the nutrient solution using polyethylene glycol （18%, w/v） and using the split root techniques. The response of net photosynthesis rate （Pn） and related photosynthetic parameters, photosynthetic pigment, chlorophyll fluorescence, foliar SOD activity and malondiadehyde （MDA） content were studied. [Result] Significantly decreased Pn, stomatal conductance, substomatal CO2, but increased leaf temperature were observed in all water-stressed plants, when compared with CK plants. However, there were no significant differences of photosynthetic pigment and MDA content, SOD activity and chlorophyll fluorescence response between CK and HRS. 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/Fo and Fv/Fm than CK from day 2 after alternating stress to roots. Significantly lower foliar photosynthetic pigment content, SOD activity, Fv/Fo and Fv/Fm, but higher foliar MDA content, were observed on WRS from day 5 or 6 after the plants were under drought stress. [Conclusion] The decreased Pn of plants under HRS should be mainly due to stomatal limitations, whereas AHRS should reduce Pn by both stomatal and non-stomatal limitations. WRS should decrease Pn mainly by stomatal limitation in the first few days after initiating water stress, and non-stomatal limitation thereafter.