Effects of atmospheric fluoride leaf uptake on plant growth, nutritional status and metabolism

Abstract

The fluoride (F) is an atmospheric pollutant that causes toxicity to plants. This is a result of metabolic disfunctions, leaf lesions and growth reduction caused to plants exposed to air pollution. The fluoride occurs naturally in soils as combined forms, even tough it is emissions of reactive compounds to the atmosphere from phosphorus fertilizer plants and ceramic industries which constitutes important via of environment contamination. Plant species that are susceptible and resistant to F toxicity are used as bioindicators to monitor environmental contaminations; susceptible plants show leaf burn, whereas tolerant ones can accumulate high concentrations of F in the leaf tissue and show no visual symptoms of toxicity. However, little is known if either metabolic or physiologic damages affect plant growth. The study of atmospheric contamination with F in the field is very complicated because of difficulty to establish comparisons between contaminated and non contaminated plants within a similar area. Considering the importance of growing citrus and coffee nearby regions of potential contamination with F, this proposal aims to evaluate the effect of F on plant processes that affect production and to compare F uptake and damages of those species with gladiolus and ryegrass. A study will be conducted under greenhouse conditions in a complete randomized design with treatments defined by two plant species and three fluoride exposure intensities (zero, low and high) replicated four times. Plants grown in 5 to 10 L pots will be exposed in a 6.12 m3 chamber with a nebulization apparatus containing HF (0.04 mol L-1 = low, and 0.12 mol L-1 = high intensity exposures). A second study will address the intraspecific response of citrus and coffee plants. Periodically, visual symptoms of F toxicity, morphologic parameters (leaf tissue structure under microscope) and physiological responses will be evaluated. Fluoride concentrations in the leaf tissue will be determined by alkaline fusion, according to modifications of standard procedures conducted in the Soil and Plant Analyses Laboratory at the Instituto Agronômico (IAC). Data will be tested by analysis of variance. The current proposal is part of a M.Sc. thesis conducted at the Graduate Program on Soils and Environmental resources at the IAC. (AU)