REACTION OF SAVANNA PLANTS FROM BOTSWANA ON UV-B RADIATION

The annual savanna grasses Chloris virgata (C-4) and Tragus berteronia nus (C-3) and the tree Acacia tortilis were exposed in a greenhouse to elevated UV-B radiation (16.8 kJ m(-2) d(-1) UV-B-Be) and to no W-B a nd grown on a poor and a rich soil for one life-cycle (grasses) and on e growing season (Acacia). W-B radiation had no effect on biomass prod uction and caryopses mass of both annual grasses. The longevity of the cotyledons of A. tortilis was shortened by 4 to 10 days under enhance d W-B radiation, which also hampered the translocation of Fe, Mg and M n from the cotyledons to the seedling and the retranslocation of Mn on both soil types and that of P on fertile soil out of senescent leaves . At the end of the growth period (190 days after germination), photos ynthesis of W-B radiated leaves of A. tortilis was significantly decre ased and supported the tendency of decreased biomass of UV-B radiated plants. It is concluded that from the investigated savanna species the grasses are relatively well adapted to increased UV-B due to their ac tual exposure to high UV-B radiation under Botswana conditions, wherea s saplings of A. tortilis are more sensitive to UV-B radiation.