The changes of PS II chlorophyll fluorescence dynamic characteristic during leaf senescence of ginkgo.

Use natural growth ginkgo leaves as experimental materials,the net photosynthetic rate,the chlorophyll content,the fluorescence emission spectra of thylakoids membranes at room temperature and the chlorophyll fluorescence parameters were measured.The results showed that photosystemⅡ(PSⅡ)function declined the same as leaf senescence.The reasons of PSⅡfunction declined were that the antenna pigment were destroyed and the receptor side of electron transfer of PSⅡwas impeded.The damaged extent of PSⅡ antenna pigments was directly proportional to net photosynthetic rate and chlorophyll content,but the center pigment structure of PSⅡwas damaged until November.With the aging of leaves,the number of PSⅡ reaction center continual decreased,in which the number of PSⅡactive reaction centers dropped 49%,but the PSⅡreaction centers only dropped 27%.It showed that the active reaction centers were more vulnerable be damaged than the reaction centers.At the side of PSⅡreceptor,the rate,the frequency and the energy needing of QA reduction continual increase.At the same time,less energy was used for electron transfer of QA downstream.Changes of chlorophyll fluorescence transient showed that the impeded electron transport chain led to PSⅡfunction descent.In November,the structure of PSⅡmostly been destroyed.