Influence of microbial associations on selenium localization and speciation in roots of Astragalus and Stanleya hyperaccumulators

► Selenium in Stanleya and Astragalus roots is most concentrated in the cortex. ► In field roots, 46-95% of Se was CSeC, with up to 35% elemental Se (Se0). ► Three fungi from field roots produced mainly Se0; these were used to inoculate. ► In greenhouse-grown plants Se0 was found only in nodules and some inoculated roots. ► Microbial symbionts appear to affect Se speciation in hyperaccumulator roots.