Abstract: In order to study the photosynthetic characteristics of different citrus cultivars, 13 citrus varieties of 6 categories were used as test materials, and the instantaneous photosynthesis parameters, response characteristics to light, response characteristics to CO₂ and photosynthetic key enzyme activities were determined and analyzed. The results showed that there were significant differences in the photosynthetic parameters and photosynthetic enzyme activities among the 13 citrus cultivars. The light compensation point and the light saturation point were between 11.99-60.00 and 523.88-1 155.73μmol·m^-2·s^-1, respectively; the CO₂ compensation point and the CO₂ saturation point were between 20.01-72.02 and 1 364.44-1 811.29 μmol·mol^-1, respectively; the Rubisco, RCA and PEPC activity were respectively between 3.74-5.34, 10.97-23.83 and 5.06-9.39 μ IU, respectively. Comprehensive analysis of different citrus photosynthetic physiological parameters and photosynthetic enzyme activity showed that the photosynthetic capacity of Hejiang Bergamot, Huangguogan and Brazil Sour orange was strong; the photosynthetic capacity of Dayagan, Wanhong blood orange and Eureka lemon were the second; the photosynthetic capacity of Ehime Kashi.38 and Hongrou Guanxi pummelo were relatively worst. Higher activity of PEPC was detected in citrus, which is a key enzyme in the C₄ photosynthetic pathway, and the ratio of PEPC to Rubisco was between 0.95-2.26, indicating that there may be a weak C₄ photosynthetic pathway in citrus.

Key words: citrus, photosynthesis, light response, CO₂ response, photosynthetic enzymes