Soil dust effects on morphological, physiological and biochemical responses of four tree species of semiarid regions

Dust pollution is expected to be a significant pollution in the urban forests, especially in semiarid environments. The purpose of this study was to evaluate the effects of soil dust on the morphological, physiological and biochemical traits of seedlings of Fraxinus rotundifolia Mill., Morus alba L., Celtis caucasica Willd. and Melia azedarach L. These species are widely grown in Iran’s urban areas, particularly in semiarid regions. The seedlings were dusted at four concentrations, 0, 300, 750 and 1500 μg m−3, once a week for 10 weeks in four plastic chambers, placed in a completely randomized design with four repetitions. Dust accumulation was greatest at the 750 and 1500 μg m−3 levels in the following order: M. alba > C. caucasica > F. rotundifolia > M. azedarach. In all species, dust decreased the leaf area, stem diameter, height, leaf, shoot, root and total biomass but increased the root–shoot ratio. Photosynthesis, transpiration, stomatal conductance, mesophyll conductance, leaf extract pH, Fv/Fm and t1/2 decreased, while leaf temperature and water use efficiency increased. Likewise, chlorophyll a, chlorophyll b, carotenoid and total chlorophyll content were diminished. M. alba has the highest soil dust accumulation potential but the lowest decrease in the properties studied. C. caucasica has a high-dust accumulation potential, but it was highly affected by dust treatment. M. azedarach and F. rotundifolia did not accumulate much dust. We conclude that among the four tree species, M. alba is the most suitable species for the urban forests of semiarid zones where dust pollution is high and dust reduction desired.