A pot experiment was conducted to study the effects of metribuzin on the chlorophyll fluorescence parameters of soybean leaves.The results showed that the fluorescence parameter NPQ was increased,and Fv/Fm,Fv/Fo,qP,ETRand the absorbed light energy showed no significantly difference compared with control at the lower application rates(630and 945g/hm2),indicating that low-concentration metribuzin treatment had certain effects on PSⅡ of soybeans,but photosynthetic intensity were not decreased obviously dependi...