Efeitos da aplicação de flúor sobre os processos fotossintéticos de três espécies lenhosas e nativas da região de Ouro Preto - MG

Abstract

Ouro Preto region (MG) receives atmospheric fluoride emission from an isolated source, an aluminum smelter. Around this fabric is located the Ecologic Station of Tripuí (EET), a preservation area limited by Atlantic forest and Savannah domains. The aim of this work was to evaluate fluoride effects on photosynthesis parameters of three native species from the EET vegetation: Eremanthus erythropappus (DC) Macleish, Tibouchina granulosa (Desr.) Cogn. and Schinus terebinthifolius Raddi. Species susceptibility and their accumulation capacity were tested, as well as the relation between leaf injuries and fluoride levels. Also, was used a control, Panicum maximum cv. Colonião, that exhibited high level of fluoride in young leaves and presented high sensibility. The plants were exposed to simulated fog with fluoride, during twenty minutes daily, for 30 consecutive days, at a simulation chamber, at the Plants Growing Unit (UFV- MG). Treatments were prepared by adding sodium fluoride (NaF) to deionized water, at a concentration of 15 mg L-1, and control plants received only deionized water (pH=6,0). The parameters related to chlorophyll a and to gas exchange were measured every five days and leaf samples were collected to determine photosynthetic pigments content and to quantify fluoride in the dry matter. In P. maximum first symptoms appeared after six days of exposure to the polluted. T. granulosa and S. terebinthifolius exhibited fist symptoms, respectively, 23 and 25 days after the beginning of the experiment. In these both species, necrosis and chlorosis were limited to apical and marginal leaf blades. Pigments alterations, that can be an important indicative of early injuries, were also evaluated at the present study. T. granulosa e S. terebinthifolius showed, after fluoride exposure, the internal CO2 concentration increases and photosynthesis and stomatal conductance decreases. Photosynthesis decreases were probably caused by stomata closure and chloroplast structure damages. Photosynthetic decreases rates were not observed in E. erythropappus but it presented variation on slow fluorescence, by the end of the treatment. Alterations on quick and slow fluorescence occurred, in both T. granulosa and S. terebinthifolius, as a response of the fluoride treatment. Images of chlorophyll a fluorescence showed that most damages were restricted to marginal leaf areas, and also decreases at Fv/Fm ration and increase at the Fo were detected in plants exposed to the pollutant. The species of this work had differentiated tolerance to the pollutant. Photosynthetic rate variations were not observed in E. erythropappu, and neither injury leaf symptoms. Also, by the end of the treatment, it showed low level of fluoride in the dry matters, which, all together, characterize this species as the most tolerant to fluoride, among the ones studied. In contrast, P. maximum accumulated the highest fluoride level in the dry matter and it was high sensitive to the pollutant, showing leaf symptoms right after few days of exposure.