Plant leaves absorb atmospheric nitrogen dioxide (NO2) primarily via the stomata. Studies of changes in plant growth and physiology after exposure to NO2 are limited. Therefore, this study investigated the physiological response of Carpinus betulus (european hornbeam) chloroplasts after NO2 exposure using fumigation equipment that was able to control timing and record NO2 concentrations. The NO2 concentration was 6 µL·L−1. Seven treatment durations (0, 1, 6, 12, 24, 48, and 72 hours) were designed. After fumigation, plants recovered for 30 days under greenhouse conditions. The physiological response, stomatal behavior, thicknesses of palisade and spongy tissues, and chloroplast ultrastructure were measured. In the 48-hour and 72-hour NO2 treatment groups, the chloroplast contents and net photosynthesis rates of the leaves decreased, palisade and spongy tissues thickened, and chloroplast thylakoids swelled; however, the 1-hour NO2 treatment did not have a noticeable toxic effect on C. betulus leaves. After 30 days of recovery, the plants returned to their natural growth level by increasing the chloroplast content and enhancing net photosynthesis. Short durations and high concentrations of NO2 exposure had significantly negative impacts on the physiological response of C. betulus; however, this toxic effect of high NO2 concentrations on C. betulus can be recovered by restoration of unpolluted air. The results of this study may provide a scientific reference and an additional choice of plants species for the application of C. betulus in functional gardening design and ecological green space construction.
Ginkgo biloba, a relict plant, has been popularized and planted in most areas of China for its leaves, timber, and fruits. In the present study, the dynamic changes in leaf color, leaf pigment content during the color change period, and photosynthetic characteristics in different growth periods were studied to explore the coloring mechanism and adaptability of five late-deciduous superior Beijing G. biloba cultivars (LD1–LD5). The results showed that the leaf color change of each superior cultivar was relatively stable, and the discoloration period of LD3 and LD5 was later than that of others. From September to November, the chlorophyll a, chlorophyll b, and total chlorophyll content in all superior cultivars showed a downward trend, except in LD3, in which the pigment content was slightly higher in October than in September. Except in LD3 and LD4, the ratio of carotene content to total chlorophyll content in other cultivars slightly decreased in October. In May, the photosynthetic capacity of LD5 was stronger than that of other cultivars. The photosynthetic capacity of LD3 was strong in July and October. Our results imply that LD3 and LD5 are suitable for mixed planting with common G. biloba to increase the overall leaf color viewing period. Ginkgo biloba leaves turn yellow in autumn because of both a decrease in the chlorophyll content after leaf senescence and an increase in the Car content during leaf senescence. Although LD5 presented rapid seedling emergence, LD3 grew faster during the vigorous and late growth stages and is thus suitable for agricultural production.