Resumo

The soil microbiota comprises a mainstay of life responsible for the ecosystems functioning and maintenance of its balance. It is believed that shifts in microbial diversity, due to soil degradation, or to use of specific agricultural practices, can influence the population dynamics and lead to the detriment of essential ecological functions, as for example, the plant colonization by mycorrhizal fungi. The purpose of this research was to evaluate the influence of the microbial community structure and diversity on the colonization of Glomus clarum in sugarcane. We have used the developed approach 'dilution to extinction', where a soil suspension was serially diluted (10-1, 10-3, 10-6, 10-9), originating cells suspensions with distinct number of cells and microbial groups. Besides the controls (sterile and natural soils), these suspensions were inoculated to sterile soils, under microcosm conditions, and amended with approximately 400 spores of the mycorrhizal fungi Glomus clarum. Sugarcane plants were planted into the pots and the experiment was monitored along 90 days. The microbial community was monitored in the original suspensions and also in inoculated soils by PCR-DGGE, indicating the differential composition of microbial communities, with a decrease in the number of bacterial and fungal bands in more diluted treatments. Together with this differentiation of the microbial diversity we could observe a shift in the rate of plant colonization by mycorrhizal fungi and a shift in plant growth parameters (root length, shoot length, dry weigh). These results suggest that sugarcane associated to mycorrhizal fungi is dependent of ecological interactions with a diverse range of fungi and bacteria living in soils, and changes in the soil diversity can direct interfere in such essential interaction involved the plant growth promotion.