Micromorphological alterations induced by simulated acid rain on the leaf surface of Joannesia princeps Vell. (Euphorbiaceae)
Guilherme Carvalho Andrade, Letícia Nalon Castro, Luzimar Campos da Silva
Abstract
Acid rain has been detected in natural protected areas of the Atlantic Rainforest in Brazil. We evaluated the effects of simulated acid rain on the leaf blade surface of Joannesia princeps, aiming to assess the species potential as biosensor of acidic precipitation. Seedlings were subjected to simulated rain prepared with pH 4.5 H2SO4-acidulated water and, in the control treatment, pH 6.0 deionized water. Severe microstructural damage was detected in the youngest leaves, consisting in wilting of epidermal common cells, which resulted on alteration of the epidermal relief due to formation of grooves among these wilted cells. Stomatal guard cells were also structurally altered, no longer presenting the turgid aspect which was visible in the control treatment. Epidermal microrelief is characterized by the presence of cuticular striae, which might have been crucial to determine the species susceptibility due to increased roughness and decreased wettability. The implications of this hypothesis are further discussed in light of recent research addressing the responses of native tree species to acid rain. The micromorphological alterations found occurred prior to the onset of visible symptoms, and therefore suggest the use of J. princeps as a biosensor of the impact by acid precipitation.