Abstract:Chlorophyll contents,net photosynthetic rates and chlorophyll fluorescence parameters of the cigar wrapper tobacco leaves were measured to study the response of photosynthetic characteristics to different N application rate under shady condition.The results showed that the chlorophyll contents of tobacco leaves were increased with the increasing rate of nitrogen,so did the PSII potential activity,the maximal photochemical efficiency of PSII,and photochemical quenching coefficient(qP) in tobacco leaves,consequently the net photosynthetic rates were enhanced.The results of experiments also showed that optimum application of N could improve the photosynthetic capability of tobacco leaves and increase the net photosynthetic rates,but over-application of N had a negative influence on photosynthetic capability and an even worse effect on the photochemical quenching coefficient and ΦPSII.