Abstract: Studying the effect of elevated atmospheric CO₂ concentration on photosynthesis and relevant physiological characteristics of pepper and revealing the relationship between atmospheric CO₂ concentration and photosynthesis and physiological indexes of pepper can provide a theoretical basis for the cultivation and fruit processing of pepper. Changes in morphological parameters, leaf physiological indexes, photosynthesis, photosynthetic pigment content, Vc content, biomass and yield in response to elevated CO₂ concentration (control level+200 μmol·mol^-1) were determined in pot experiment using an open-top chamber (OTC) experimental facility. The results showed that the elevated CO₂ concentration promoted the growth of pepper and increased plant height, yield and total biomass. At elevated CO₂ concentration, leaf net photosynthetic rate (P_n), intercellular CO₂ concentration (C_i) and water use efficiency (WUE) increased, stomatal conductance (G_s) and transpiration rate (T_r) increased in blossom and fruit period while decreased during fruiting stage. Elevated CO₂ concentration also significantly increased Vc content in the leaves and fruits and the contents of chlorophyll and carbohydrate in the leaves of pepper. Elevated CO₂ concentration improved the photosynthetic system and increased the photosynthesis of pepper leaves, and then promoted the accumulation of metabolic substances, which are beneficial to the growth and development of pepper.

Key words: ROS system, SA pathway, defense enzyme gene., JA pathway, defense enzyme