Abstract

Cluster roots are modifications of the root system developed by some plants as a strategy to increase the availability of nutrients in the soil through the exudation of carboxylates. Embothrium coccineum is an endemic species to Southern South America bearing cluster roots, which chemically and biochemically modify their rhizosphere depending on their developmental stage. We evaluated how cluster roots shape microbial diversity according to their developmental stage. We determined genetic and metabolic profiles of bacterial communities from bulk soil, root soil (close to E. coccineum roots), and rhizosphere soil from non-cluster roots and cluster roots in different developmental stages (i.e. juvenile, mature, semi-senescent, and senescent). In addition, the exudation rates of mature and non-cluster roots and the chemical characteristics from bulk and root soils were assessed. Root soil had higher nitrate and potassium contents and was more acidic than bulk soil probably due to the carboxylates exuded by the root system. These edaphic properties were related to differences in microbial community diversity. At the genetic level, the communities associated with the juvenile cluster roots presented a significantly different profile from those derived from the rest of the rhizosphere. Conversely, at the metabolic level, the carbon sources' consumption profiles of the senescent cluster roots were significantly different from the others. Our results suggest a selection or recruitment of microorganisms at the beginning of the development of E. coccineum cluster roots and a succession of metabolic capabilities of the microbial community throughout the development of cluster roots.