中文摘要：

为了比较秋季不同衰老时期苹果叶片光合生理特性的差异，以生草覆盖条件下5年生苹果园为对象，研究了不同衰老时期叶片的叶绿素、可溶性蛋白质、超氧阴离子、丙二醛的含量和超氧化物歧化酶活性及光合荧光参数的差异。结果表明，叶片净光合速率（Pn）随衰老程度的加剧而显著降低。与衰老初期相比，中后期叶片J相相对可变荧光（K）显著升高、最大荧光（Fm）显著降低，说明PsⅡ的基本结构和功能受到了严重破坏；捕获的激子用来推动电子传递链中超过级的激子所占比率（ψo）和用于电子传递的量子产额（φEo）显著降低、PsⅡ最大光化学效率（Fv／Fm）变化平稳，说明光合机构通过调控Fv／Fm来维持较高水平的ψo和φEo在衰老后期，可变荧光Fk占Fj-Fo振幅的比例（Wk）和Vj急剧升高，初始荧光（Fo）、Fm、ψo、φEo和Fv/Fm急剧降低，ψo、φEo和Fv/Fm分别为初期的29．7％、11．3％和38．0％，说明叶片PsⅡ的基本结构受到了严重破坏，功能基本丧失。

英文摘要：

In order to compare differences of photosynthetic physiological characteristics of different aging-stage apple leaves in fall, taking 5-year-old apple trees under grass coverage management as study objects, the contents of chlorophyll, soluble protein, superoxide anion and malondialdehyde （MDA）, superoxide dismutase activity and photosynthetic fluorescence parameters in leaves during leaf senescence stage were researched. The results show that the Pn is significantly reduced with aging-degree increasing. Compared with the early stage of leaf aging, relative variable fluorescence at J-phrase （Vj） at the middle and later stages of leaf aging is significantly increased, but the maximum fluorescence （Fm） is significantly decreased, which indicates that basic structure and function of PSII are seriously damaged. Efficiency with which a trapped exciton can move an electron into the electron transport chain fiarther than QA （ψo） and quantum yield for electron transport （φEo） at the middle and later stages of leaf aging are significantly decreased, and the PS II maximum photochemical efficiency （Fv/Fm） is changed insignificantly which indicates that photosynthetic apparatus can regulate the Fv/Fm to maintain a higher level of ψo and φEo. At the late stage of leaf aging, ratio of variable fluorescence Fk to the amplitude Fj-Fo （Wk） and Vj are sharply increased, original fluorescence （Fo）, Fm, ψo, φEo and Fv/Fm are sharply decreased, and ψo, φEo, Fv/Fm are 29.7%, 11.3% and 38.0% of that at early stage, respectively, which indicates that basic structure ofPS Ⅱ are broken up, and the functions are lost.