Avaliação dos efeitos do fogo nas relações funcionais entre a vegetação e fertilidade do solo em Campo Rupestre sobre quartzito

Abstract

The Campo Rupestre on quartzitic soil in Serra da Calçada, Minas Gerais, an area that belongs to an integral protection conservation unit, suffered a great impact due to the circulation of motocross and jeep, which resulted in loss of vegetation and erosion of its springs. In the initial phase of recovery of the degraded areas, a site adjacent to them was hit by an intense fire, which was an additional factor of impact. Thus, the study of plant biodiversity and soil fertility at the burned area, 12 months after the fire, became necessary since this area may constitute a source of propagule for the area undergoing recovery. The study areas: preserved, burned and degraded were compared in relation to the distribution, abundance and richness of families and plant species, as well as soil physicochemical fertility and mycorrhizal colonization of established plants. In the burned area, there was a great decrease in the richness of species and families, in the diversity index, and an increase of grasses concentration, besides the presence of the invasive Melinis minutiflora (Poaceae). Soil analyzes for the burned area showed a decrease in organic matter, CTC, K, Mn and NH4+ when compared with the preserved area. It was also observed a significant increase of Na and of NO3- as a result of the fire. Considering that in the preserved area, the concentrations of Na and NO3- are low and that the native vegetation prefer the ammoniacal chemical form, the increase in the nitrate and sodium concentrations in the burned site, seems to have exerted a selective pressure altering the composition of the biodiversity. The area reached by fire showed a low mycorrhizal colonization of plant roots, together with the absence of Orchidaceae plants and their associations with arbuscular mycorrhizal (AMF) and orchid fungi (OMF), possibly contributed to the divergent succession of the patterns of the preserved area. It is concluded, therefore, that after a year of the occurrence of fire, the biodiversity was not only reduced, but also the composition of this biodiversity was altered. These alterations were attributed to the increase of nitrate and sodium content in the soil in detriment of the ammoniacal chemical species, followed by lost of mycorrhzal network as well as the loss of function of part of the organic matter, resulting in a decrease in CTC. Such changes can also modify the succession in the degraded area under recovery and, therefore, recovery of the burned area is recommended.