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

Three sclerophyllous Ericaceae (Erica curvirostris Salisb., E.fairii Bolus and E. nudiflora L.) found on nutrient-impoverished soils, but at different elevations, were grown for 4 months in a greenhouse under three different daily doses of biologically effective ultraviolet-B (u.v.-B) radiation, namely 7.8, 9.4 and 11.4 kJ/m2, which approximated present ozone conditions and 10 and 20% depletions in the ozone layer, respectively, at 33-degrees-56'S, 18-degrees-20'E. Significantly reduced pollen germination and pollen tube growth were observed in vitro under white light in pollen samples collected before anthesis from plants exposed to increased u.v.-B radiation. A significantly reduced net CO2 assimilation rate at enhanced u.v.-B radiation levels was observed in E. fairii only, a species restricted to low elevations. This was attributed to an increased stomatal limitation, since stomatal conductances declined, apparent carboxylation efficiency (ACE) increased and apparent quantum efficiency (AQE) remained unchanged with increased u.v.-B radiation. ACE, AQE and stomatal conductances increased in E. nudiflora, but this was not reflected significantly in net CO2 assimilation rate. Dark respiration increased only in E. curvirostris. Water potentials, water use efficiencies and specific leaf weights of all species were unaffected by enhanced u.\-.-B radiation levels, though transpiration increased in E. curvirostris due to an increased stomatal conductance. The general physiological insensitivity of Ericaceae to increased u.v.-B radiation may be related to the structural, physiological and chemical properties of their sclerophyllous leaves and their low growth rates.