Brazilian Conference on Natural Products
7th Brazilian Conference on Natural Product/ XXXIII RESEM Proceedings

The exploitation of ores such as iron, bauxite and manganese brings social and economic benefits to the Brazilian states, especially in the northern region, but it generates environmental damage that is difficult to remedy despite current environmental legislation. In the state of Pará, a bauxite mining company is evaluating different methodologies for restoring areas after exploration. Among the methodologies practiced, the main ones are: Natural Regeneration, Plant Seedlings and Nucleation. Natural Regeneration consists in covering the degraded area with the superficial forest soil existing in the area before the bauxite exploration (top soil) and allowing the seeds present in this soil to germinate. At Planting, the area that was explored receives a thin layer of top soil and seedlings of native plants of that region while in Nucleation, the top soil is used to make small “basins”, which are covered by antlers of the removed native vegetation forming small shelters for birds and other animals that eventually bring seeds from elsewhere, contributing to species diversity. In this work the areas subjected to these three methodologies, in different stages of development, are being compared with areas of native forest and recently deforested areas based on soil microbiota, especially the group of free-living nitrogen-fixing microorganisms. For the analyzes, soil samples were collected in these areas in two seasons: at the height of the drought (September 2018) and at the peak of the rain (April 2019). Using selective culture media for each functional group of microorganisms, the samples were diluted and inoculated and colony abundance and diversity counts were performed. Considering the free-living nitrogen-fixing microorganisms, the diversity in forest environments (considered as control in this work) in the dry season is very low and the abundance of the surviving groups is high. In this period of analysis, the areas that most resembled the forest areas in this group of microorganisms were those under the natural regeneration and nucleation method. In the areas without vegetation (suppression) the presence of nitrogen-fixing microorganisms was not observed and, in the planting areas, the diversity of this group was greatly reduced. In the rainy season, the diversity of microorganisms in the soil is very high in the forest areas, in this parameter, none of the recovering areas resembles the control areas. The largest abundance of free-living Nitrogen fixators at this time was observed in old areas with seedling planting. The oldest studied areas are regenerating for ten years, this period was not enough for the diversity of nitrogen-fixing microorganisms to return to the same as in the forests there. Time is the essence for the dynamics of this microorganisms group to begin to return to their natural state. Since the largest differences between areas were observed in the dry season, this may be considered the best time for this comparison and, considering diversity and abundance of free-living nitrogen-fixing microorganisms, the area most similar to forest areas is natural regeneration old area.