Abstract: The effects and differences of three treatments including strong light（25 ℃，1 400 µmol · m^-2 · s^-1），high temperature（45 ℃，700 µmol · m^-2 · s^-1）and strong light coupled with high temperature（45 ℃，1 400 µmol · m^-2 · s^-1）on photosystem in leaves of tree peony（Paeonia suffruticosa‘Juanyehong’）were studied，respectively. The results indicated that both the maximum photochemical efficiency（F_v/F_m）and activity of PSⅠ（ΔI/I_o）obviously reduced under three treatments，and the decrease of ΔI/I_o was quicker than that of F_v/F_m within 2 h. With the increasing of treatment duration，the ability of electron transfer from PSⅡ to PSⅠ（φ_Eo）reduced. Under strong light stress，the number of reaction centers per unit area（RC/CS_m）displayed decrease，and difference of the ability of electron transfer（V_J）was not significant. Under high temperature stress，the main injured region tended to the PSⅡ receptor side，and the ability of electron transfer from PSⅡ to PSⅠwas depressed，which resulted in that excess light energy under unsaturated light affected the activity of PSⅡ reaction center and reduced the absorption of light energy（ABS/CS_m），the capture of light energy（TR/CS_m）and the energy quantum yield of electron transfer in reaction center（ET/CS_m）. Compared with single stress，strong light coupled with high temperature aggravated the photoinhibition，but the activity of PSⅡ reaction center had no significant difference under single and cross stress in the early stage（≤ 1 h）. The results indicated that the effect of cross stress was not the simple superposition of two single stress.

Key words: tree peony, photosystem, strong light and high temperature, photoinhibition