Influence of crust-covered paving on photosynthesis and chlorophyll fluorescence parameters of a city landscape plant, <Emphasis Type="Italic">Firmiana simplex</Emphasis>

In order to explore the influence of crust-covered paving on city landscape plants, the photosynthesis and chlorophyll fluorescence parameters of Firmiana simplex were studied in this paper by the LCI portable plant photosynthesis meter and the OS5-FL-mode pulse modulated chlorophyll fluorometer. The results showed that during the day, the net photosynthetic rates of Firmiana simplex leaves under the crust-covering stress were slightly lower than those of the control, and the differences were significant at 18:00; the transpiration rate of the treatment group showed a single-peak curve, with the peak appearing between 12:00–14:00, while the transpiration rate of the control group showed a bimodal curve with the peak appearing at 10:00 and 16:00, respectively. When the transpiration rate of the control showed a low peak at 14:00, the transpiration rate of treatments was very significantly higher, and the difference was as much as 45.08%. In addition to 16:00 of all day, the water use efficiency of Firmiana simplex leaves under crust-covered condition was slightly higher than that of the control; the differences were not significant in the morning but very significant in the afternoon. The stomatal conductance of treatments was significantly higher than that of the control at 14:00 and slightly lower than the control at any other time. The intercellular CO2 concentration of treatments was higher than that of the control during the day except at 16:00, and the difference was significant at 14:00 and 18:00. The maximal photochemical efficiency of PS II (Fv/Fm) and the potential activity of PS II (Fv/Fo) of treatments were both lower than those of the control during the day except at 18:00, with very significant differences at 14:00. By this token, we concluded that the crust-covered paving had somehow brought a certain stress to the city landscape plant, Firmiana simplex.