SURFACE DUST IMPACTS ON GAS-EXCHANGE IN MOJAVE DESERT SHRUBS

1. Windblown dust, an environmental problem in many disturbed arid lan ds, has the potential to affect the physiological performance of deser t shrubs. Physiological parameters of gas exchange for three species ( Larrea tridentata, Hymenoclea salsola and Atriplex canescens) were mea sured at a Mojave Desert site, at which both undisturbed and heavily d usted individual shrubs occurred. 2. Maximum rates of net photosynthes is (A) of dusted organs were reduced to 21% of those of control plants in resinous leaflets of Larrea, to 44% in resinous leaves and photosy nthetic stems of Hymenoclea, and to 58% in non-resinous C-4 leaves of Atriplex, which have vesiculated trichomes. Dusted plants of all three species showed reduced maximum leaf conductance (g(s)), transpiration (E) and instantaneous water-use efficiency (A/E). Intrinsic water-use efficiency (A/g(s)) was also reduced, except in Atriplex, in which it remained unchanged.3. Temperatures of dusted leaves and photosyntheti c stems were 2-3 degrees C higher than those of control plants, due to greater absorptance of infra-red radiation. Dust also significantly i ncreased photosynthetically active radiation (PAR) reflectance. 4. Hea vily dusted shrubs had smaller leaf areas and greater leaf-specific ma sses, suggesting that the short-term effects of reduced photosynthesis and decreased water-use efficiency may cause lowered primary producti on in desert plants exposed to dust during seasons when photosynthesis is occurring.