CONCENTRATION OF ULTRAVIOLET-B RADIATION ABSORBING COMPOUNDS IN LEAVES OF A RANGE OF FYNBOS SPECIES

Leaves from 38 species representing 17 families were collected from co ntrasting elevations (100 to 824 m above sea level) in sclerophyllous mountain fynbos vegetation near Hermanus, South Africa, and the leaf p ercentage dry mass (PDM), specific leaf mass (SLM) and ultraviolet-B ( UV-B, 280 to 320 nm) absorbance properties determined. Leaf PDM, SLM a nd UV-B absorbance were generally high compared to mesophyllous plants . Leaves collected at high elevation exhibited higher absorbances per unit dry mass at both 280 and 320 nm than those from the same species at low elevation. No differences in absorbance per unit leaf area were observed. UV-B absorbance properties differed between families, with high values obtained for the Apiaceae, Asteraceae, Cyperaceae, Ericace ae, Penaeaceae and Proteaceae, but lower values for the Anacardiaceae, Fabaceae and Geraniaceae. A positive correlation was found between ab sorbance at 280 nm per unit leaf area and SLM. It was concluded that m ost fynbos species, on account of their highly sclerophyllous leaves a nd large accumulation of UV-B absorbing compounds (flavonoids and rela ted phenolics) may be well protected against future increases in UV-B radiation.