Speciation of Selenium in the Rhizosphere of Symphyotrichum Eatonii in Reclaimed Mine Soils.

Plant-availability of Se to aster (Symphyotrichum eatonii (A. Gray) G.L. Nesom) was measured in extractions and compared in rhizosphere soils and bulk soils collected from a reclaimed phosphorus mine in southeastern Idaho, USA.  X-ray absoirption micro-spectroscopy was used to characterize the oxidation state and elemental distribution of Se in aster roots, rhizosphere soils, and bulk soils.  Extractable Se in aster rhizosphere soil was greater than extractable Se in corresponding bulk soils in all samples.  Oxidation state mapping indicated that reduced Se(-II,0) predominated in the rhizosphere of the aster, while in the root tissues high concentrations of Se(VI) accumulated.  Data support plant-enhanced Se bioavailability and root surface oxidation of reduced soil Se in the rhizosphere.