RESPONSES OF SCLEROPHYLLOUS ERICACEAE TO ENHANCED LEVELS OF ULTRAVIOLET-B RADIATION

Three sclerophyllous Ericaceae (Erica curvirostris Salisb., E.fairii B olus and E. nudiflora L.) found on nutrient-impoverished soils, but at different elevations, were grown for 4 months in a greenhouse under t hree different daily doses of biologically effective ultraviolet-B (u. v.-B) radiation, namely 7.8, 9.4 and 11.4 kJ/m2, which approximated pr esent ozone conditions and 10 and 20% depletions in the ozone layer, r espectively, at 33-degrees-56'S, 18-degrees-20'E. Significantly reduce d pollen germination and pollen tube growth were observed in vitro und er white light in pollen samples collected before anthesis from plants exposed to increased u.v.-B radiation. A significantly reduced net CO 2 assimilation rate at enhanced u.v.-B radiation levels was observed i n E. fairii only, a species restricted to low elevations. This was att ributed to an increased stomatal limitation, since stomatal conductanc es declined, apparent carboxylation efficiency (ACE) increased and app arent quantum efficiency (AQE) remained unchanged with increased u.v.- B radiation. ACE, AQE and stomatal conductances increased in E. nudifl ora, but this was not reflected significantly in net CO2 assimilation rate. Dark respiration increased only in E. curvirostris. Water potent ials, water use efficiencies and specific leaf weights of all species were unaffected by enhanced u.\-.-B radiation levels, though transpira tion increased in E. curvirostris due to an increased stomatal conduct ance. The general physiological insensitivity of Ericaceae to increase d u.v.-B radiation may be related to the structural, physiological and chemical properties of their sclerophyllous leaves and their low grow th rates.