Efeito da deposição da poeira de cimento na estrutura foliar, ultraestrutura celular e em variáveis fisiológicas e bioquímicas de espécies lenhosas nativas

The present study focused on native woody species in the state of Minas Gerais, Brazil, occurring in areas of limestone outcrops, which have received in over years particulate matter from cement factories activities. The work evaluated the effects of cement dust on the structural and ultrastructural organization of the leaf and in physiological and biochemical variables of Cedrela fissilis Vell. (Meliaceae), Guazuma ulmifolia Lam. (Malvaceae), Myracrodruon urundeuva Allemão (Anacardiaceae) and Trichilia hirta L. (Meliaceae). To this end, plants were exposed to concentrations of 0; 2.5 and 5 mg cm-2 of cement particulate matter applied at two moments on the leaf surface; on the soil and the leaf surface and soil, in controlled exposure conditions and standardized soil. Among the studied species, there was differential tolerance for the cement dust, and C. fissilis was the one with the highest susceptibility, which led to the closure of the experiment with this species at 41 days after the start of the simulations, differing from other species (60 days) considered tolerant to dust. In C. fissilis, in the treatments with alkaline particulate matter on the plant shoot, there was chlorosis and leaf necrosis, senescence, leaflets curling and fall off, increased enzyme activities of the antioxidant system, reduction in stomatal conductance and in the potential quantum yield of photosystem II, among other symptoms. For all four plant species, after application of dust, there was cement crust formation on the leaf surface, blockade of part of the incident light and obstruction of the stomata, besides changes in the levels of photosynthetic pigments, in morphoanatomy and nutritional composition, with reduction in the foliar content of Fe, among other symptoms. In general, the harmful effects of dust were prior to possible changes in pH and chemical composition of the soil, being caused mainly due to the contact of the cement with the leaf surface. The results obtained may support strategies for the conservation and recovery of impacted areas by cement factories, which represent a threat to local biodiversity.