中文摘要：

探讨清耕栽培苹果叶片衰老过程中PSⅡ荧光诱导动力学的变化,为延迟叶片衰老技术的应用提供理论依据。以清耕栽培‘寒富’苹果为试材,采用气体交换和叶绿素荧光诱导动力学分析技术,研究了叶片衰老过程中叶绿素含量、净光合速率（Pn）和PSⅡ荧光诱导动力学的变化。结果表明,9月30日~10月20日,光合机构通过调控单位面积PSⅡ反应中心数（RC/CSo）、活性反应中心数量（RC/ABS）、捕获的激子中用来推动电子传递链中超过QA的激子所占比率（ψo）和用于电子传递的量子产额（φEo）维持较高的PSⅡ的最大光化学效率（Fv/Fm）;10月30日叶片I相和P相荧光强度明显降低,J相相对可变荧光（Vj）显著升高,说明PSⅡ的基本结构和功能受到严重破坏;11月9日叶片K相、J相、I相和P相荧光强度显著降低,可变荧光Fk占Fj-Fo振幅的比例（Wk）和Vj急剧上升,说明PSⅡ基本结构被瓦解、功能已丧失。因此,延缓叶片衰老的技术措施应于10月20日之前使用。

英文摘要：

The changes of chlorophyll a fluorescence transient during senescence of apple leaves under bare earth condition were stud- ied in order to provide theoretical basis for the application of delayed leaf senescence technology. The present study measured the chan- ges of chlorophyll content, net photosynthetic rate, and chlorophyll fluorescence parameters during leaf senescence of Hanfu＇apple un- der bare earth conditions, using gas exchange analysis and chlorophyll a fluorescence induction kinetics analysis. The results showed that photosynthetic apparatus through the regulation of density of PSII reaction centers per excited cross section （ RC/CSo） , number of active reaction centers per energy absorbed（ RC/ABS）, efficiency with which a trapped exciton can move an electron into the electron transport chain further than Qs - （ ψo ） and quantum yield for electron transport （ φro ） to maintain a higher PS II maximum photochem- ical emciency （ Fv/Fm） from September 30 to October 20. In October 30, fluorescence intensity of I and P phrases of leaves were sig- nificantly declined, and relative variable fluorescence at J - phrase was significantly increased, which indicated that basic structure and function of PSII were seriously damaged. In November 9, fluorescence intensity of K, J, I and P phrases were significantly declined, ratio of variable fluorescence Fk to the amplitude Fj - Fo and Vj were sharply increased, which indicated that basic structure of PS II were broken up, and the functions were lost. Hence, the delayed leaf senescence technology should be applied before October 20.