Soil selenium uptake and root system development in plant taxa differing in Se-accumulating capability.

•  Phytoremediation of Se-contaminated soils and sediments may be more feasible if accumulating taxa are identified that can extract the more refractory forms of Se. •  In a glasshouse study, the capacity of six plant genotypes to take up labile and nonlabile soil Se was evaluated by amending five high-Se soils (2-21 mg kg-1 total Se) with carrier-free 75 Se, and cropping them with Astragalus bisulcatus, Astragalus canadensis, Brassica juncea, Sporobolus airoides, and two ecotypes of Stanleya pinnata. •  The biologically labile pool of soil Se (L-value) was computed from the isotopic signature of the harvested shoots, and ranged from 2 to 37% of the total soil Se. The chemically labile pool (E-value) was determined via extraction in 0.1 m KCl, and ranged from 4 to 73% of total soil Se. None of the plants tested yielded L-values that were consistently greater than the E-values, suggesting that all plants, including Se hyperaccumulators, access the same labile pools of Se. •  Root-growth experiments in rhizoboxes using Se-enriched soil were also performed. Although our observations were not as striking as those made for the Zn(Cd)-accumulator Thlaspi caerulescens, the tendency for roots of some Se-accumulators to proliferate in soil where Se is present deserves further investigation.