Abstract: The light response curves and CO₂ response curves of Caragana microphylla and Salix gordejevii in the dunemeadow transitional area of Horqin sandy land were measured using a Li-6400XT portable photosynthesis system. The measured data were fitted using a rectangular hyperbola model, a nonrectangular hyperbola model, and a modified rectangular hyperbola model of the photosynthetic response to light and intercellular CO₂ concentration, respectively. The results showed that the modified rectangular hyperbola model could better fit the light response and CO₂ response curves. However, there were significant differences in photosynthetic characteristic parameters between the two plants, due to the effects of the desert environment. C. microphylla showed a lower light compensation point and CO₂ compensation point, but a higher light saturation point than S. gordejevii. This suggested that C. microphylla had a stronger ability to adapt to the environment. The apparent quantum yield of S. gordejevii was greater than that of C. microphylla, which indicated that S. gordejevii had a high conversion efficiency of light energy. In addition, C. microphylla presented a lower rate of dark respiration than that of S. gordejevii. When the CO₂ concentration reached saturation, the maximum net photosynthetic rates of C. microphylla and S. gordejevii were 44.5 and 29.7 μmol·m^-2·s^-1 respectively, which were 3.98 and 1.87 times of those under saturation light. A habitat with highCO₂ concentration promoted the growth of S. gordejevii, while C. microphylla formed the accumulation of organic matter at a lower CO₂ concentration. At the same time, C. microphylla had high efficiency of carboxylation and a strong ability of CO₂ assimilation.

Key words: ozone dry deposition flux, ozone deposition resistance., ozone deposition, ozone dry deposition rate