Ora-pro-nobis (Pereskia aculeata Mill.) Nutrition as Related to Soil Chemical and Physical Attributes and Plant Growth-Promoting Microorganisms

The objective of this study was to evaluate the relationship of nutrients in Ora-pro-nobis to the physical-chemical attributes and the communities of N2-fixing bacteria and arbuscular mycorrhizal fungi of the soils in the southern part of the state of Minas Gerais, Brazil. Rhizospheric soil, root, and leaf samples were collected from 12 sampling points in four neighboring municipalities. N2-fixing bacteria from rhizospheric soil, roots, and washed roots macerated in water were isolated using a N-free semi-solid medium, and the 16S rRNA gene was sequenced. Arbuscular mycorrhizal fungi spores were extracted from the soil by the wet-sieving method, followed by sucrose-gradient centrifugation. The collected roots were cleared and analyzed according to the traditional methods for the evaluation of mycorrhizal colonization. The soil samples and leaves were analyzed for physical-chemical and chemical attributes, respectively. There was no relationship between the total nitrogen in the soil and the protein content (based on N content) in the leaf of Ora-pro-nobis as well as between the concentration of the other nutrients in the leaf and their corresponding concentration in the soil, except for potassium and magnesium. Of the 86 isolates obtained, 70 were identified in the genus of the N2-fixing bacteria Azospirillum. There was a variation in spore density and mycorrhizal colonization. The families Ambisporaceae, Archaeosporaceae, Claroideogloraceae, Glomeraceae, Acaulosporaceae, Diversisporaceae, and Gigasporaceae were identified. Associative N2-fixing bacteria and arbuscular mycorrhizal fungi were abundantly found in close relationship with Ora-pro-nobis, which may explain the ability of this plant to sustain high protein content in its leaves even in soils with relatively low nitrogen concentration.