Plant morphology and photosynthesis can serve as indicators of how well a plant will react to urban air pollution. The physiological photosynthetic response of plant leaves to NO₂, a characteristic contaminant in vehicle exhaust from urban roads, was studied in this study. The intelligent artificial fumigation chamber was used to simulate the biennial Bougainvillea spectabilis seedlings (NO₂ volume fraction was 0 μL/L (natural air), 4 μL/L, and 8 μL/L, labeled as CK, T1, and T2).After NO₂ stress, we looked at the leaf morphology, microstructure, and photosynthetic traits of B. spectabilis. The findings revealed that:(1) It was discovered that the low concentration T1 group's leaves underwent minimal alteration in comparison to CK. The leaves in the high concentration T2 group gradually lost water as the concentration of NO₂ gas stressed them, leaving either clear water stains or cauterized yellow patches on the leaf surface. (2) Leaf microstructure study revealed that under conditions of high NO₂ stress, the extent of stomatal shrinking increased and stomatal openness reduced. Chloroplast structure changes, particularly the loosening and enlargement of the thylakoid structure.(3) Leaf photosynthetic characteristics study revealed that NO₂ stress in the T1 and T2 groups decreased the maximum net photosynthetic rate (P_nmax) and the light saturation point (LSP), while increasing the light compensation point (LCP). There were differences between the four light response models in terms of apparent quantum efficiency (AQE) and dark respiration rate (Rd). (4) Among the four light response models, the CK group had the highest accuracy, the lowest root mean square error, and the highest coefficient of determination (R²) among the four. Particularly, the rectangular hyperbola model comes in second place to the leaf drift mechanism model in terms of best fitting performance.Our study's findings demonstrate that B. spectabilis may adapt to varying NO₂ concentrations, notably high concentrations under acute stress, by changing its morphology and photosynthetic characteristic characteristics.The findings will assist spread awareness of and use of various road greenbelt B. spectabilis. It is crucial to understand B. spectabilis' ecological and spatial advantages as well as its process of adaptation in order to better understand environmental heterogeneity.