Microbiota edafica como indicadora da reabilitação de áreas contaminadas por elementos-traço

Abstract

World development has caused great industrial activity increase and consequently diverse non-environmentally sound practices such as diverse types of contamination. Mining areas are the most relevant contamination sources, due to the disposal of large amounts of residues containing high trace elements concentration. This activity can have detrimental effects on diverse microbial communities that play an important role on ecosystem sustainability. Therefore, it is important to develop soil rehabilitation practices for vegetation to be established, thus allowing restoration of diversity and functionality of soil microrganisms. In this context, this work aimed to evaluate soil microbial communities as indicator of rehabilitation of areas contaminated by trace elements in the municipality of Três Marias-MG. It was evaluated: bacteria, actinobacteria and fungi densities, arbuscular mycorrhizal fungi (AMF) occurrence and diversity, and bacteria and fungi diversity by Denaturing Gradient Gel Electrophoresis (DGGE) of 16 S rDNA gene and ITS regions and sequencing of ITS regions for selected fungal isolates. The rehabilitated studied areas were: 1: replacement of surface soil layer and plantation of Eucalyptus camaldulensis, in lines (A1L) without planting rows (A1EL); 2: replacement of soil surface layer and plantation of E. camaldulensis, in lines (A2L) and Brachiaria decumbens in rows (A2EL). The rehabilitated areas were compared to adjacent non-contaminated areas of Cerrado (C) and Pasture (P) as well as to and a highly contaminated area without vegetation (SV). Results have shown that bacteria, actinobacteria and fungi densities increased after rehabilitation practices at levels similar to non contaminated areas. Spore number and AMF diversity were higher in rehabilitated areas when compared to areas C, P and SV. Glomus was the only genus occurring in all rehabilitated, non rehabilitated and non contaminated areas. The analysis of DGGE showed a greater similarity in the profiles of bacterial communities than in the fungal profile communities of the diverse areas. The diversity of bacteria and fungi increased in the rehabilitated rehabilitated areas compared with the area SV. Sequences of fungal isolates from the area with higher concentration of trace elements were identified as belonging to the following species: Aspergillus brasiliensis, Penicillium brefeldianum, P. purpurogenum, P. citrinum and P. variabile. All biological parameters studied were shown to be good indicators of the rehabilitation practices by the replacement of surface soil layer and revegetation.