Influência de elementos terras raras em características anatômicas em plantas de arroz, milho, trigo e feijão

Abstract

Rare earth elements (ETRs) include lanthanides, yttrium and scandium, are used in high technology products and "clean technologies". In addition, these elements are present in fertilizers, having promoted higher yield and quality of agricultural crops, mainly in China. In Brazil, is one of the largest agricultural producers and consumer of phosphate fertilizers, producing large-scale rice, beans, corn and wheat, which are the basis of food. The objective of this work was to evaluate the effects of the application of ETR on the anatomy of cultivated plants (rice, wheat, corn and beans). The foliar doses from a solution of ETR (containing La, Ce, Pr and Nd) were as follows: rice 0; 0.1; 0.25; 0.5 and 1 kg ha-1; for maize: 0; 0.1; 0.3; 0.6 and 1.2 kg ha-1; for wheat: 0; 0.1; 0.3; 0.6, 1.2, 2.4 and 4.8 kg ha-1. For the beans, four fertilizers containing ETR: pure ammonium phosphate salt and formulated commercial, Araxá and Catalão were evaluated via soil. The second experimental factor in the beans was doses of P2O5, which consisted of four doses (0, 40, 80, and 160 kg ha-1). For the anatomical evaluations, the material was collected, fixed in F.A.A.70%, stored in 70% ethanol and submitted to a series of ethanolic dehydration for subsequent infiltration and inclusion in hydroxyethyl methacrylate Leica®. The cross sections were made with the aid of a rotating microtome and obtained material was stained and mounted in permanent, and than evaluated. From the histometric data obtained, the averages were compared by the Scott-Knott test, with a 5% significance using the Sisvar software. In rice, the application of ETR caused thickening of the epidermis, reductions of mesophyll, diameter of metaxylem. Differently from that observed for rice, the application of ETR provided an increase of foliar tissues in maize plants, as well as reduction in stomatal indices accompanied by the density of the stomata only on the adaxial side, possibly because it is a more resistant culture and better adaptability to the stresses. In wheat, reductions in leaf tissue thickness were more evident as a sign of toxicity. In bean, the application of pure salt to the soil showed values similarto commercial formulations, showing that the highest concentrations of ETR had responses in the sense of reducing the thickness of the foliar tissues and thickening the roots, mitigating possible negative effects of these elements. For future research, it is suggested to focus on foliar concentrations up to 0.3 kg ha-1 for maize, wheat and rice, to avoiding effects related to toxicity. For the bean, the application between 40 and 80 kg ha-1 of P2O5 and the formulations of Araxá and Catalão can be good sources of P and benefit the crop by the presence of ETR.