Seleção de isolados de bactérias de solos de caatinga com potencial para promoção de crescimento vegetal

Abstract

Desertification is characterized by the degradation of arid, semi-arid and dry sub-humid lands, induced by climatic factors and anthropic activities. In Brazil, 60% of the semiarid region is considered susceptible to desertification and, in the state of Ceara, the municipality of Irauçuba is the most affected by the process. Microorganisms can be a tool for the restoration of these areas as they act in several soil processes. Thus, the objective of the study was to evaluate the edaphic variables and metabolic activities of bacterial isolates of soils in three different stages of conservation in the municipality of Irauçuba: a) soils of secondary forest of caatinga; b) grazing exclusion soils, isolated since 2000; c) overgrazing soils. The soils were sampled in 2018. Once in the laboratory, soil physical and chemical properties were analyzed and 125 bacteria were also isolated from these samples. The isolates were tested for several assays of Plant Growth Promoters, among them: Production of siderophores, using agar-CAS medium; phosphate solubilization, using GL medium with addition of K2HPO4 and CaCl2; the positive isolates for one or both assays were tested for nitrogen fixation, using the semi-solid medium LGI-P free of nitrogen and halotolerance, using TGE medium with different salt concentrations. A higher percentage of phosphate solubilizing bacteria was observed in the native area, in contrast to the desert soil, where the lowest percentage was noticed. About 50% of the isolates produced siderophores, regardless of the area. The grazing exclusion area showed the best results in relation to the quality of production and solubilization of these compounds. At least 60% of the isolates, regardless of the area, were able to fix nitrogen, and all isolates were considered halotolerant. The main soil problems are related to the predictors of salinity. The grazing exclusion soils have significantly distanced themselves from the overgrazing situation and tend to approach the natural area or present an intermediate recovery profile, which indicates a positive effect of fallow on these soils. Sixteen isolates were selected for sequencing and phylogenetic analysis for the excellent results for plant growth promoters, the isolates belong to the genera: Klebsiella; Serratia; Enterobacter and Burkholderia. We aim to apply these isolates to produce bio inoculants that can accelerate the recovery of degraded environments in Irauçuba-CE and mitigate the advance of the desertification process in the municipality.