Surface Dust Impacts on Gas Exchange in Mojave Desert Shrubs

Windblown dust, an environmental problem in many disturbed arid lands, has the potential to affect the physiological performance of desert shrubs. Physiological parameters of gas exchange for three species (Larrea tridentata, Hymenoclea salsola and Atriplex canescens) were measured at a Mojave Desert site, at which both undisturbed and heavily dusted individual shrubs occurred. Maximum rates of net photosynthesis (A) of dusted organs were reduced to 21% of those of control plants in resinous leaflets of Larrea, to 44% in resinous leaves and photosynthetic 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. Temperatures of dusted leaves and photosynthetic stems were 2-3°C higher than those of control plants, due to greater absorptance of infra-red radiation. Dust also significantly increased photosynthetically active radiation (PAR) reflectance. Heavily dusted shrubs had smaller leaf areas and greater leaf-specific masses, suggesting that the short-term effects of reduced photosynthesis and decreased water-use efficiency may cause lowered primary production in desert plants exposed to dust during seasons when photosynthesis is occurring.