Soil quality indicators showed recovery of an iron mining area compared to adjacent phytophysiognomies

Abstract

Mining activities modify the landscape and can generate environmental impacts on the soil, water and air, necessitating that these sites that have undergone the mining process be rehabilitated through revegetation processes. After rehabilitation, the areas should be evaluated for the degree of recovery or disturbance. Microbiological indicators are the most sensitive tools for these assessments. Therefore, the objective of this study was to evaluate soil microbiological indicators of an area rehabilitated after iron mining activities and to compare with adjacent non-disturbed phytophysiognomies. Soil samples were collected in the Canga (Ironstone Outcrops – IO), Cerrado (Neotropical Savanna – NS) and Atlantic Forest (AF) and an area rehabilitated after iron mining with grass (RA), in two climatic seasons (dry and rainy) in the Quadrilátero Ferrífero - MG - Brazil. The soil attributes evaluated were the microbiological, chemical and physical. The microbiological indicators differed according to the type of vegetation and the season of the year. AF was the phytophysiognomy that exhibited higher values of microbial biomass and of enzymatic activities. The IO and NS exhibited an active microbial biomass in the nutrient cycling processes evidenced by the enzymatic activities. RA showed a positive effect of revegetation by providing greater specific enzymatic activities by carbon of the microbial biomass and higher microbial coefficient, as well as the greater symbiotic efficiency of plant growth promoter rhizobacterial communities. Microbiological attributes, organic carbon, total nitrogen, Fe2+, Cu2+ and Al3+, pH, potential acidity, cation exchange capacity and sand and clay content were sensitive to indicate differences between phytophysiognomies. A total of 327 strains were isolated at both seasons. Genetic diversity was evaluated by partial sequencing the 16S rRNA gene, from which 29 genera were identified in the dry season and 18 in the rainy season. The genotypes Bradyrhizobium, Rhizobium and the endophytic Paenebacillus were the most frequent in both seasons and phytophysiognomies. The richness of genera found in the areas in the dry and rainy season were respectively 8 and 6 in IO, 6 and 8 in NS, 11 and 15 in AF, 15 and 7 in RA. The process of rehabilitation of areas after iron mining by revegetation with grass is being effective in soil recovery, evidenced by high specific enzymatic activities by microbial biomass and the symbiotic efficiency of the rhizobacteria community promoting plant growth in this soil.