Caracterização ambiental e avaliação de Cyperus ligularis L. (CYPERACEAE) na recuperação de áreas afetadas pela atividade de mineração de zinco

Abstract

According to the Brazilian environmental law, mining areas must be recovered after exploitation. The presence of phytoavailable trace elements in high concentrations in the soil can affect vegetation normal development. The use of native species should be considered to recovery these areas, since it reduces the environment disturbance and can facilitates the reestablishment of loca l biodiversity. The study was conducted aim to revegetate a mine of zinc (Zn) disabled. The mine soil is heterogeneous and the area was divided into six points which are most representative of its general conditions. Each point has different semitotal and phytoavailable contents of Zn, cadmium (Cd), and lead (Pb), and these contents exceed the value of prevention established by law. A floristic survey found 82 species of 28 botanical families. Many of these families are represented by only one species, corr esponding to 21% of the floristic composition. This shows the low richness of the area. However, the adverse conditions in which these plants are found, and considering the high number of native species (89%), it appears that the revegetation of the area is possible. Cyperus ligularis L. was found in two of these points. The absorption capacity of soil contaminants and the anatomy of fundamental vegetative organs of C. ligularis found in contaminated areas were studied attempting to identify explanations of their natural occurrence in these conditions. The results show that C. ligularis is tolerant to Zn, Cd and Pb, therefore it is recommend this plant for the recovery areas containing high phytoavailable content of these elements. This species has greater ability to translocate the elements to the shoots in waterlogged environments. The presence of trace elements in the soil induces cortex thickening and the root endoderm as protective mechanisms against translocation. In waterlogged environments, the highes t translocations of Cd and Zn resulted in bigger bulliform cells and in thicker mesophyll by the increase of the aerenchyma proportion. In contaminated not -waterlogged environments, reducing the system's vulnerability index decreases Zn and Cd translocatio n and increases Pb bioaccumulation. Subsequently, it was done studies aiming at the use of the species in the revegetation of three other mining areas. The species produces large number of viable seeds. The germination test showed that these seeds of the species do not grow well in all areas. The high phytoavailability of trace elements in the soil inhibits germination and the presence of Cd most related to the loss of seedlings in the first days. The high Pb content in the soil primarily affects the germination speed. Thus, the seed rain technique is not recommended in one of the areas (A4). The seedlings transplant test showed that C. ligularis can be used to revegetate contaminated areas. In this study, it was used seedlings of the species produced in commercial substrate. After transplant, the plants show slow growth in soils containing higher Pb content. High Cd concentrations inhibit the formation of aerenchyma in the roots. The delay in the formation of these structures does not interfere in the plant growth. It is recommended the transplant use of seedlings in the revegetate areas, especially in sites where germination does not occur due to the high content of trace elements. The seedlings transplant test showed that C. ligularis can be used to revegetate contaminated areas. In this study, it was used seedlings produced in commercial substrate. After the transplant, the plants show slow growth in soils containing higher Pb content. High Cd concentrations inhibit the formation of aerenchyma in the roots. The delay in the formation of these structures does not interfere in the plant growth. Anatomical modifications, both in the roots and in the leaves, follow the standard of the growth rate of C. ligularis. However, in roots the high bioaccumulation of Pb and the translocation of all trace elements induce the formation of epidermis and cortex thicker root. Despite the reduction in the growth rate, plants that have had high translocation of Cd have leaves with bigger buliform cells. It is recommended the transplant use of seedlings to revegetate areas, especially in sites where germination does not occur due to the high content of trace elements.