Elementos terras raras na fisiologia, nutrição e crescimento da soja

Abstract

Strategic for high technology, the rare earth elements (REE) are a group of elements having similar physical and chemical characteristics. These elements are called earth rare by their occurrence in the form of oxides, and because the difficulties of individualization in the analysis process, but, the abundance in the lithosphere is relatively high. They can exchange calcium at phosphate minerals and be added to the soil through the fertilizers. In this direction, soybean is one of the crops which receive the most phosphate fertilizers, then, frequent applications of these elements can be found. Thus, the objective of this study were to evaluate: 1) bioaccumulation and effects of lanthanum (La) on growth and mitotic index; 2) bioaccumulation and effects of samarium (Sm), gadolinium (Gd) and neodymium (Nd ) on the growth and nutritional changes of soybean under these elements; aiming to provide a better understanding about of possible mechanisms of that plants subjected to REE and to examine the beneficial or toxic potential of REE. The results of the first experiment showed a biphasic effect of application of lanthanum, depending of concentrations, stimulations in shoot production and roots at low concentrations was observed, as well as elevation in photosynthetic rate, increase in the total chlorophyll content and increased incidence of binucleated cells. Decreased growth was detected and ultrastructural changes in the cell wall, thylakoids and chloroplasts. In this study, we observed roots biomass sixty times higher than shoots. In future, is suggested to use concentrations less than 10 µM for tests with La in nutrient solution. The second experimental results showed that the application of Sm, Nd and Gd in nutrient solution at the levels studied did not provide substantial biomass gains in soybean plants. The application of rare earth elements (Sm, Gd and Nd) affect the nutritional balance of soybean plant, especially the increase in the P content and P accumulation of whole plant. The gains in photosynthetic rate and accumulation of some nutrients did not result in increase of biomass, because the toxic effect of Sm, Gd and Nd at the higher levels are interfering decisively in the construction of biomass plants due stress occasioned under these elements. In general, it is concluded that the application of REE isolated in nutrient solution has different aspects depending on the element and REE concentrations.