Seleção de características morfofisiológicas no biomonitoramento das chuvas ácida ou fluoretada em duas espécies arbóreas

Abstract

This study aimed to evaluate the effects of simulated rain, acid and with fluoride, separately, on leaves of Plinia cauliflora and Cupania vernalis, assessing alterations in morphology, ultrastructure and chlorophyll a fluorescence, besides analyzing the content of fluoride in dry leaves of these species, in order to provide subsidies for the use of these plants in the biomonitoring of environments contaminated by these pollutants. For the simulated acid rain bioassay, seedlings of P. cauliflora and C. vernalis were exposed to simulated rain at pH 6.0 (control) and pH 3.0 (treatment) for 15 minutes during 10 consecutive days. Similarly, for the bioassay of simulated fluoridated rain, seedlings of P. cauliflora and C. vernalis were exposed to simulated rain containing 0, 10, 15 and 20 mg L-1 of KF for 15 minutes during 10 consecutive days. During the experiment, it was evaluated the fluorescence of chlorophyll a, in the dark and light and, at the end of the simulations, leaves were collected to quantify the content of F in the dry mass; leaves and leaf fragments were also colected for analysis by light microscopy and scanning electron microscopy. No changes were detected in the thickness of any tissues P. caulifora and C. vernalis after the simulation of the both bioassays. After the end of experiment, only P. cauliflora presented chlorosis and necrotic spots on the edge of some leaves when exposed to simulated acid rain and only the C. vernalis presented chlorosis simulation of fluoridated rain, the damage being more accentuate at concentrations 15 and 20 mg L-1 KF. At the ultrastructural level, erosion and formation of epicuticular wax were detected, as well as leaf surface colonization by fungal hyphae in the two bioassays in both species. After the end of the simulations, it was possible to verify that the both simulated rain, did not significantly affect any of the evaluated characteristics of chlorophyll a fluorescence in P. cauliflora. Nevertheless, for C. vernalis, it was detected a reduction in the potential quantum yield of PSII (Fv/Fm), for both bioassays. For the simulation of fluoridated rain, it was observed increase in the coefficient of non-photochemical quenching (NPQ) in the highest concentrations of KF. Both species accumulated fluoride content in their tissues and all treatments differed from each other. These results demonstrate that P. cauliflora and C. vernalis present potential to be used as biosensors for monitoring the occurrence of rain, acid and with fluoride or like as ecological indicators by bioaccumulation of fluoride in the atmosphere. The species P. cauliflora, which has shown to be more resistant to fluoride is promising to be used in areas impacted by this type of pollution.