Abstract:

The increase in UV-B radiation and airborne SO2 has become a serious environmental issue. In this paper the photosynthetic responses of 20 species of common tropical and subtropical greening trees to supplementary UV-B radiation and/or SO2 (simulated by sulfite solution) were studied. Trees were grown under natural conditions in the South China Botanic Garden. The relative resistances of these trees were estimated through the photosynthesis and chlorophyll fluorescence characteristics. Leaves were collected from the canopy of the 20 species and treated with UV-B radiation, NaHCO3 and UV-B+NaHCO3 for 72 h in the laboratory. Photosynthetic O2 evolution rate of these isolated leaves was then measured by leaf disc oxygen electrode system (Hansatech, King’s Lynn, UK), and their fluorescence emission (Fv/Fm) was tested using a PAM-Fluorometer (Walz, Effeltrich, Germany). Results showed that these plants can be classified into three types: high resistance, medium resistance and sensitive according to their resistant abilities to supplementary UV-B and/or SO2. They further showed that the UV-B radiation damage to the trees could be enhanced by treatment with SO2. The inhibition induced from a single stress factor, SO2 or UV-B, had a positive relationship with that from combined factors, UV-B+NaHCO3, in these tested trees. The response of chlorophyll fluorescence characteristics of these trees to environmental stress and applications of this technique for studying forest ecology, environmental physiology and stress physiology were also discussed.