Resumo

Phosphorus (P) is a key element for the maintenance of life, from the processes of energy transfer (ATP) to the structure of the chains of nucleic acids. It is often the most limiting vegetative growth factor due to the high reactivity of PO₄^3- in the soil solution. More than 80% of P added to the soil can be immobilized in the form of compounds with low lability, by adsorbance to the surfaces of clays and Fe³⁺ and Al³⁺ oxy-hydroxides, a irreversible process under natural conditions. The solubilization of non-labile P to plants is possible through the release of organic acids released by natural micro-organisms in the soil, which also effectively contribute to the mineralization of P-organic production, however, these mechanisms are still poorly understood. The main objective of this study was to analyze the bacterial communities structure associated with the rhizosphere of sugarcane related to the addition of different P-sources. The experiment was conducted in a greenhouse (ambient condition), with plants grown in pots containing 10 kg of a poor oxisol on phosphorus, which had its pH adjusted with lime and high base saturation to 60%. Treatments were conducted with the addition of three P sources (Triple superphosphate, monoammonium phosphate and reactive phosphate of Gafsa). The fertilizers were applied at a rate of 180 kg ha^-1 P₂O₅, taking into account the solubility of the individual content sources and the P. Furthermore, treatments were conducted with and without addition of filter cake (4.0 t ha^-1). The plants were harvested after four months and removed from the vessel for determination of root and shoot dry weight. The rhizosphere bacterial communities structure were analyzed through DGGE (denaturing gradiente gel eletroforese). According to the results the treatment added with monoammonium phosphate showed the greatest response of culture, especially regarding the shoot, showing an embodiment of mass greater than the other treatments, both with and without filter cake. Futhermore was observed that the different forms of phosphate fertilizers influence the structure of microbial communities associated with the rhizosphere of sugarcane as well as the addition of filter cake, which can also be related to the incorporation of organic matter to the soil-plant. The mechanisms linking soil chemistry with the behavior of micro-organisms associated with plants are not well known, being further purpose of this study the phylogenetic characterization of the most important species as well as their roles in the process of solubilization, mineralization and availability of P in soil.