Abstract: Under field condition, this paper measured the leaf gas exchange parameters and photosynthetic pigments content of different drought-resistance wheat varieties at all growth stages, with their responses to different nitrogen fertilization levels studied. The results showed that in treatment N₁₈₀, the leaf G_s, P_n, and total photosynthetic pigments content of dry land varieties increased by 43.75%, 18.54% and 49.66%, while those of watered land varieties increased by 12.12%, 20.88% and 29.25%, respectively, compared with control. On the contrary, the respiration rate of dry land and watered land varieties decreased by 4.8% and 4.5%, respectively. Nitrogen supply accelerated the photosynthetic carbon assimilation, because the gas exchange capacity and photosynthetic pigments content increased while the respiration rate decreased with increasing nitrogen supply. The difference in photosynthetic capacity between different winter varieties was mainly dependent on non--stomatal factors. The dry land varieties had higher capacities of light energy absorption and photosynthetic carbon assimilation, because they had higher leaf photosynthetic pigments content but lower respiration rate. Compared with watered land varieties, dry land varieties had an 8.9% decrease of respiration rate and a 14.12% increase of P_n. At the same growth stage, the photosynthetic and respiration rates in the control varied consistently, while in treatments N₁₈₀ and N₃₆₀, the photosynthetic rate increased but the respiration rate decreased. Nitrogen fertilization promoted the absorbed light energy allocating to the process of photosynthetic carbon assimilation. It could be concluded that nitrogen supply was favorable to the improvement of winter wheat drought-resistance, because it could improve leaf gas exchange capacity, increase leaf photosynthetic pigments content, and optimize the allocation of absorbed light energy.

Key words: Earthworm, Methamidophos, Acetochlor, Cu, Combined pollution, Ecological toxicity