Toxidez do alumínio em caju-de-árvore-do-cerrado (Anacardium othonianum Rizz.)

Abstract

The evaluation of the toxicity caused by aluminum plants in the Brazilian cerrado regions has great importance for the development of agriculture, because these areas are dominated by oxisols, which are acid soils with low cation exchange capacity, high exchangeable aluminum saturation and very low phosphorus available to plants. Little attention has been given to communities of native cerrado plants that tolerate acid soil conditions, such as the species Anacardium othonianum Rizz., fruit plant and popularly known as the tree cashew of the cerrado, with many food, nutritional and medicinal applications. Thus, the aim of this study was to evaluate the effects of aluminum on root growth, nutrient accumulation and root structure of seedlings of A. othonianum Rizz. The germinated seedlings were growth in a nutrient solution only composed of 0,1 mM CaCl2.2H2O, and also in a complete low ionic strength solution, both with concentrations of aluminum (0, 150, 300, 600 and 1200 μM) nutrient solution. Subsequently, the seedlings were evaluated for root growth, root elongation, dry mass and anatomical studies using techniques of light and fluorescence microscopy field. Emergence percentage and speed index emergence seedlings using washed sand moistened with a solution of aluminum in different concentrations were also assessed. The results showed that aluminum caused a reduction in the rate of root growth and root elongation relative phytotoxicity being observed from 150 μM Al in solution. Reduction in the rate of emergence rate, percentage of seedlings emergence and anatomical changes in root tips, particularly in meristematic regions was also observed being demonstrated stimulation of these cells with vacuolization and internalization of aluminum in different tissues. Aluminum decreased absorption of most nutrients in the seedlings, with the following order of reduction in roots: P> Ca> Mg> N for macronutrients and Fe> Cu for micronutrients; reduction in leaves followed the order: Ca> Mg> P. On the other hand, higher concentrations of aluminum increased N and K content in leaves and Mn in roots. The K content in roots, and Fe, Cu and Mn in leaves were not affected by concentrations of aluminum. The results showed that this species tolerates high concentrations of aluminum, but the fall in rates of root growth and nutrient content can reduced the production of nut and pseudofruit in acid soils with high concentrations of this element, since the reduction in root growth makes plant operates less volume of soil, which in turn affects water and nutrient absorption.