Photosynthetic Responses of Plants to Supplementary UV-B Radiation and Sulfite and Their Resistances

Abstract

The increase in UVB radiation and airborne SO_(2) has become a serious environmental issue. In this paper the photosynthetic responses of 20 species of common tropical and subtropical greening trees to supplementaiy UVB radiation and/or SO_(2)(simulated by sulfite solution) were studied. Trees were grown under natural conditions in the South China T3otanic 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 UVB radiation, NaHCO_(3) and UVB+NaHCO_(3) for 72h in the laboratory. Photosynthetic O_(2) 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 UVB and/or SO_(2). They further showed that the UVB radiation damage to the trees could be enhanced by treatment with SO_(2).The inhibition induced from a single stress factor, SO_(2) or UVB, had a positive relationship with that from combined factors, UVB+NaHCO_(3), in these tested trees. The response of chlorophyll fluorescence char acteristics of these trees to environmental stress and applications of this technique for studying forest ecology, environmental physiology and stress physiology were also discussed.