Abstract: Ground-level ozone (O₃) is considered as a secondary air pollutant with strong oxidative toxicity to plants, which causes serious damage to plant photosynthetic system and impedes forest carbon sequestration. In this study, based on leaf-scale chlorophyll fluorescence imaging technology, the open-top chambers were used to measure photosynthesis fluorescent parameters and investigate ozone dose-response relationships of four urban greening tree species (Fraxinus chinensis, Platanus orientalis, Robinia pseudoacacia, and Sophora japonica) in Beijing. The results showed that with the increases of O₃ concentration, the maximum photon yield of PSⅡ reaction center (QY_max), the steady-state light adaptive non-photochemical fluorescence quenching coefficient (NPQ_Lss), the steady-state fluorescence attenuation parameter (Rfd_Lss), the actual photochemical quantum efficiency of PSⅡ reaction center (PhiPS2_Lss) and the photostable maximum photon efficiency of PSⅡ reaction center (F_v′/F_m′) decreased significantly, while the steady-state light adaptive photochemical fluorescence quenching coefficient (q_PLss) did not change. Except for Rfd_Lss, there were significant differences in chlorophyll fluorescence parameters among different greening tree species. All the four species showed a significant negative correlation between fluorescence parameters and the O₃ dose index AOT40 (cumulative value of hourly ozone concentration exceeding 40 nmol·mol^-1). The chlorophyll fluorescence imaging of the whole leaf reflected the process that the PSII reaction center was gradually damaged with the increases of O₃ dose, and the reduction of photosynthetic capacity followed the order from leaf margin to leaf mesophyll to leaf vein. Chlorophyll fluorescence imaging technology could reflect the spatiotemporal response characteristics of plants to O₃ stress on leaf scale, with certain application prospect.

Key words: ozone, dose, greening tree species, chlorophyll fluorescence, linear relationship.