In this study, we used poplar as a model plant and investigated the effects of gaseous nitrogen dioxide (NO 2 , 4 µl 1 −1 ) on stomatal conductance, photosynthesis, dark- and photorespiration of Populus alba × Populus berolinensis hybrid leaves using the photosynthesis system and scanning electron microscope technique. The results showed that net photosynthetic rates were significantly reduced in leaves exposed to 4 µl 1 −1 NO 2 for 48 h as compared with leaves exposed to ambient carbon dioxide 380 µl 1 −1 and ambient NO 2 <0.1 µl 1 −1 (the control) and the leaves exposed for 14 h. The decline of net photosynthetic rate was caused mainly by NO 2 treatment. Dark respiration rates were dependent on co-action of the two factors (leaf temperature and NO 2 treatment time). Post-illumination carbon dioxide burst in the exposed leaves occurred at 13–15 s after turning the light off, whereas this phenomenon was absent in the control leaves.