Abstract: Abstract: A fast chlorophyll transient fluorescence and its dynamic parameters were measured by a PEA (Plant Efficiency Analyzer from Hansatech), in the leaves of Ginkgo ( Ginkgo biloba ) after illumination of strong light with chilling stress or heat stress, respectively. In addition, a response of light on LCE (light conversion efficiency of photosynthesis) was measured by a CIRAS-2 of the portable photosynthesis systems. The results indicated that photoinhibition in leaves of Ginkgo showed a dosage effect of not only the light intensity but also the temperature. LCE was lowest and showed more serious photoinhibition over about 1 000 μmol m^-2s^-1 PAR (photosynthetic available radiation). At 25 ℃, F_v / F_m in the leaves of Ginkgo showed accelerating decline after illuminating for 20 min at PAR 1 000 μmol m^-2s^-1 or more on the leaf of Ginkgo, and the F_v / F_m showed more serious decline at low temperature of 15 ℃ or lower and high temperature of 35 ℃ higher. Meanwhile, photoinhibition exhibited more serious when treated by chilling stress than by heat stress, because absolute value of the slope of linear regression equation ( k_heat ) between F_v / F_m and temperature form 25 ℃ to 45 ℃ increased 15.4% than absolute value of k_chilling from 20 ℃ to 5 ℃. The strong light caused a modest little increase of energy dissipation DI_o /RC at chilling stress of 5～10 ℃, but a sharp increase of that at heat stress of 35 ℃ or higher 35 ℃. Density of PS Ⅱreaction centers decreased at chilling stress, but it decreased more serious at heat stress than at chilling stress. There were remarkable correlations between photoinhibition ( F_v / F_m ) caused by strong light at chilling stress and heat stress and density of PS Ⅱreaction centers ( RC/CS_o or RC/ABS ). Therefore, the heterogeneity of PSⅡ, i.e. reversible inactivation of PSⅡ reaction center, is protection mechanism on photoinhibition of the photosynthesis apparatus.

Key words: Key words: chilling stress, heat stress, chlorophyll fluorescence parameter, photosystem Ⅱ, photoinhibition, ginkgo