Eficiência de comunidades e diversidade de rizóbios em área sob influência da mineração de ferro em Minas Gerais

Abstract

The study of soil biodiversity has become increasingly important due to the impacts of anthropic action and the increase in world demand for food, since microorganisms are indicators of soil quality and important tools to improve the agricultural production process. In order to evaluate the diversity and efficiency of rhizobia communities in different vegetations in the "Iron Quadrangle of Minas Gerais", soils were collected in areas of "Iron Outcrops", "Atlantic Forest", "Neotropical Savanah" and "Rehabilitaded área revegetated with grass". The symbiotic efficiency of the communities was evaluated in a greenhouse experiment using cowpea (Vigna unguiculata) as bait plant, and the data obtained were correlated with chemical and physical attributes of the soils under each type of vegetation. At the end of the experiment, the bacteria present in the nodules were isolated to evaluate biodiversity. The highest and lowest number of nodules occurred in soils under Grass and Neotropical savanah vegetation and Iron outcrops and Atlantic Forest, respectively. In relation to the root dry matter, the soil under Neotropical savanah vegetation was superior to the other areas. In relation to the shoot dry matter there was no significant difference between the treatments. The soil attributes with the greatest influence on the microbial communities were aluminum content, considered high under Atlantic forest and Neotropical savanah vegetation, medium in Iron outcrops and very low in Grass; organic matter, which presented very high values in Iron outcrops and Neotropical savanah, high in Atlantic forest and low in Grass; the pH under Grass indicated average level of acidity, under Iron outcrops and Neotropical savanah high acidity and under Atlantic forest very high acidity. Through isolation of nodules, 380 bacterial strains were obtained and separated into 27 culture groups by cultural characterization analysis. Genetic diversity was evaluated by the 16S rRNA gene partial sequencing of 89 strains, which were identified as belonging to nitrogen-fixing Leguminosae nodulating bacteria (NFLNB) genera (Rhizobium, Bradyrhizobium and Burkholderia), representatives of associative bactéria (Bacillus, Paenibacillus, Herbaspirillum, Pseudomonas and Agrobacterium) and other genus (Brevibacillus, Novosphingobium and Chitinophaga).