Occurrence of vesicular-arbuscular mycorrhizae in agro and natural ecosystems of Minas Gerais State

Abstract

The occurrence of vesicular-arbuscular mycorrhizae (VAM) was evaluated in rhizosphere samples of plants representatives of several agro and ecosystems located at 41 counties of the 'Triângulo', 'Norte' and 'Sul' regions of the state of Minas Gerais, in Brazil. One hundred and sixty-five samples of soil and roots of plants were collected during the summer. Roots were separated from the soil, stained, and used for determinating the rate of mycorrhizal colonization. Soil was used for spore extraction of VAM fungi and for chemical analysis. The presence of root colonization or spores of VAM on the soil were detected in every sample. The rate of mycorrhizal colonization ranged from 0 in one sample of Eucaliptus to 91% on Macraptilium, and spore density ranged from 0 to 277 per 50 ml of soil. In the natural ecosystems the mean colonization was 13% while in all agroecosystems it was higher than 36%. Spore density was twice as much higher in agroecosystems than in natural ecosystems, where an average of 19 fungi species were found, against 12 in the agroecosystems. Acaulospora morrowae, A. scrobiculata, A. spinosa, Gigaspora sp, G. pellucida, Glomus etunicatum, G. diaphanum, and Entrophospora colombiana were the predominant species. A. morrowae and A. scrobiculata were twice as abundant in agroecosystems than in the natural ecosystems. In contrast, all other species were less abundant in the agroecosystems than in the natural ecosystems. Changes in species composition seem to reflect changes in soil chemical properties, resulting from crop practices, such as plowing, liming, and fertilization.