Leaf Plasticity Responses of Four Urban Garden Plants to Low-Light Environments Under Viaducts

The low-light environments under urban viaducts significantly hinder plant growth and development. An in-depth study of the plasticity response mechanisms and survival strategies of plants in these conditions is crucial for selecting appropriate species. This study examined how light intensity affects leaf plasticity in four plants (Ophiopogon japonicus, Pittosporum tobira, Euonymus japonicus, and Ligustrum sinense) under two representative urban viaducts and how they respond to changes in light intensity in Zhengzhou City. The leaf morphology, physiological photosynthesis, and chlorophyll (Chl) fluorescence parameters were analyzed at three light intensities (one natural full-light and two viaduct-shaded low-light environments.): CK (full light), T1 (21.29%–25.99%), and T2 (5.16%–8.20%). The results showed that (1) with decreasing light intensity, most plants showed reductions in leaf thickness (LT), palisade and spongy tissue thickness (PT, ST), net photosynthetic rate (Pn), stomatal conductance (Gs), and Fv/Fm and Fv′/Fm′, while leaf area, Chl content, and malondialdehyde (MDA) content increase, with antioxidant enzyme activity also rising. The photosynthetic indicators of O. japonicus first increased and then decreased. (2) The overall plasticity of the plants ranked from high to low as follows: O. japonicus > E. japonicus > P. tobira > L. sinense. O. japonicus showed the strongest adaptability through comprehensive photosynthetic physiology and antioxidant mechanisms, with a wide light tolerance range. E. japonicus relied more on adjustments in photosynthetic and anatomical structures, as well as leaf area. P. tobira improved light tolerance by modifying leaf area, epidermal structure, and physiological traits. L. sinense had the lowest adaptability, relying on limited antioxidant enzymes and leaf thickness adjustments. (3) In conclusion, plant plasticity is primarily reflected through photosynthetic and physiological traits. High plasticity in these parameters is key for plants to adapt to thrive in dynamic low-light environments. Therefore, when greening viaduct-shaded areas, it is crucial to consider the light environment and the light adaptability range of different plant species. Plants with high photosynthetic and physiological plasticity should be selected to ensure the optimal growth and development of plants in shaded areas.