Abstract: L ight2dependent chlorophyll fluorescence characteristics of leaves in the four Euphorbia
pulcherrim a cultivars‘J induoli’,‘ChristmasAngel’,‘SonoraWhite Glitte’and‘Royal Red’were exp lored
using the chlorophyll fluorescence technique. The results indicated that the minimal fluorescence ( Fo ) , the
maximal fluorescence ( Fm ) and the variable fluorescence ( Fv ) of‘J induoli’were extremely significant
higher than the other cultivars. The changing trend of relative electron transport rate ( rETR) , the effective
quantum yield of PSⅡ (Yield) and photochemical quenching ( qP ) were identical under the photosynthetically
active radiation ( PAR ) from 0 to 2 171μmol·m- 2 ·s- 1 , which showed ‘J induoli’ > ‘ChristmasAngel’
> ‘SonoraWhite Glitte’ > ‘Royal Red’. And the differences of these valueswere more evident under the
high PAR. There were the same trend to the maximal relative electron transport rate ( rETRmax ) , half2satura2
tion light intensity ( Ik) and photoinhibition parameter (β) among cultivars. All those revealed that‘J induo2
li’had higher PSⅡ activity and was able to tolerate strong irradiance; And‘Flag’, which has lower photo2
synthesis efficiency was easier appearance to suffer photoinhibition.

Key words: Euphorbia pu lcherrim a, chlorophyll fluorescence, rap id light response curve