Effects of building shade on photosynthesis and chlorophyll fluorescence of Euonymus fortunei

Urban shading is caused by artificial urban construction and has different effects on the photosynthesis of plant, and this shading will affect the plants in photosynthesis. The purpose of the study was to reveal the plant photosynthetic characteristics in urban shading, provide theoretical basis for improving the ecological benefits of urban vegetation and provide scientific basis for urban plant landscape configuration. We selected leaf samples of Euonymus fortunei from three typical urban light environments: full natural light, part-time shade and full urban building shade. We quantified various measures of photosynthesis and chlorophyll fluorescence using the CIRAS-2 photosynthesis and FMS-2 fluorescence systems, respectively. The results indicated that urban shading by artificial structures caused differences in both the spatial and temporal distribution of photosynthetic active radiation (PAR). Surprisingly, this was not due to differences to the air temperature (Ta), relative humidity and CO2 concentrations, which were consistent among the light conditions. Urban building shade also caused changes in leaf morphology and chloroplast pigment content of E. fortunei. Leaf area (LA) increased with part-time shade and decreased with full shade, while lamina mass per unit area (LMA) decreased significantly as the shade increased. Chlorophyll b content increased and the chlorophyll a/b ratio decreased with the decrease of PAR. Pn of E. fortunei displayed an irregular single-peak curve under full light and part-time shade, and the peak for each appeared at 10:00 and 12:00, respectively. Pn displayed a double-peak curve under full shade, with peaks appearing at 10:00 and 16:00. Tr of E. fortunei was significantly correlated with Pn. The Pn-PAR curve showed that Pmax, LSP, LCP, and Rd all decreased along with PAR, with the exception of AQY, which significantly increased. Chlorophyll fluorescence parameters also changed under the different light environments. Fo and ΦPSII both increased with the decreases in PAR, but Fv/Fm and NPQ decreased. Different levels of urban shading caused the changes in adaptive strategies of E. fortunei. When there was no direct sunlight appearing, a highest level of shading, E. fortunei presented obvious adaptive changes in its physiological photosynthetic processes, morphology, photosynthetic pigments and so on, and this type of the greatest shading caused by urban buildings or other infrastructures can obviously affect the growth of plants.