Diversidade de isolados bacterianos e sua influência na FBN em diferentes coberturas vegetais

Abstract

The diversity of soil microorganisms interact directly with the vegetation cover. Legumes play a fundamental role in soil fertility by adding nitrogen contributing to the maintenance and balance of the ecosystems. The main scope of this study was to evaluate the effect of vegetation on rhizobia diversity for effective nodulation and N2 fixation in the tree legumes: leucena (Leucaena leucocephala (Lam.) De Wit.) and sabiá (Mimosa caesalpiniifolia Benth.) grown in a Luvisol from the semiarid region of Pernambuco state, Brazil. Samples were collected in the field in soil submitted to different vegetation cover (leucena, sabiá, preserved caatinga, savannah and intercropping maize-beans). A greenhouse experiment was carried out with the soil samples grown leucena and mimosa tree legumes. The isolates obtained from the root nodules were morphologically characterized and grouped to study the diversity, by the construction of dendrograms and calculate the diversity index. The capacity of nitrogen fixation by leucena and mimosa was assessed by means of the natural abundance of 15N. There was a great diversity among bacterial isolates regarding their morphological and physiological characteristics showing a diverse population varying with the different vegetation cover. Soils with vegetation cover less disturbed showed the best results in biological nitrogen fixation and leucena displayed the highest percentage of N2 fixation evaluated by the natural abundance of 15N, especially in soils under savannah vegetation and preserved caatinga.