Annals of Botany 90: 127-137, 2002
© 2002 Annals of Botany Company
Effects of Elevated Ultraviolet-B Radiation on Native and Cultivated Plants of Southern Africa
1 Research and Scientific Services, National Botanical Institute, Private Bag X7, Claremont 7735, Cape Town, South Africa and 2 Botany Department, University of Cape Town, Private Bag, Rondebosh 7701, South Africa
* For correspondence. Fax +21 797 6903, e-mail musil{at}nbict.nbi.ac.za
Received: 11 February 2002; Returned for revision: 4 March 2002; Accepted: 10 April 2002
Seventeen herb, shrub and tree species of commercial and ecological importance in southern Africa were exposed at one location to ultraviolet-B (UV-B, 280–315 nm) radiation approx. 35 % above clear-sky background (control). The aims were to assess how UV-B affects canopy area, dry mass, and some biochemical and morphological properties of leaves, and to investigate whether differences between species are related to growth form of the plants. There was no pattern of response to UV-B related to growth form. Leaves of trees had altered chlorophyll a and b, carotenoid and flavonoid concentrations, but those of shrubs or herbs did not. Non-structural carbohydrates were unaffected. Smaller canopy areas and dry masses were observed under enhanced UV-B, but these were not statistically different among growth forms. There was a general insensitivity of species to elevated UV-B. Only five species had significantly altered leaf biochemical and morphological properties, canopy area and dry mass, the changes differing in magnitude. There was no consistent pattern of change in leaf thickness or biochemical composition with increased UV-B. Correlation analyses did not support the view that growth is less negatively affected in species with thick leaves or in those where leaf thickness increases, or in species with naturally high leaf flavonoid contents or that are able to synthesize additional flavonoids in response to UV-B enhancement. The analyses did not support the hypothesis that growth was inhibited by starch accumulation in leaves under elevated UV-B. However, changes in leaf shape did correlate with canopy area and dry mass, showing the importance of photomorphogenetic changes caused by UV-B which affect species’ performance. We conclude that generalizations on plant sensitivity to UV-B based on growth form and functional type could be misleading, and that the great majority of economically important species of the region are likely to be insensitive to future UV-B increases. Notable exceptions include the Colophospermum mopane tree ecotypes chota and leslie and the arable annual Vigna unguiculata, both of which are traditional sources of livelihood to rural African populations and of importance to African industry and agriculture.
Key words: African plant, carbohydrate, chlorophyll, flavonoid, growth, leaf area, morphology, plant growth form, ultraviolet-B radiation, Colophospermum mopane, Virgilia oroboides, Leucadendron laureolum, Podalyria calyptrata, Protea burchellii, Cliffortia ruscifolia, Hermania saccilifera, Phylica pubescens, Aspalathus linearis, Barleria obtusa, Cyclopia genistoides Glycine max, Phaseolus vulgaris, Vigna subterranea, Vigna unguiculata, Lupinus luteus, Vicia atropurpurea.