Transfer of REEs from nutrient solution to radish through fine roots and their distribution in the plant

In order to clarify transfer of rare earth elements (REEs, La through Lu) from soil solution to a plant and their distribution in the plant, a preliminary study on plant uptake of REEs was carried out using nutrient solution. Radish seedlings grown in a nutrient solution culture for about a month were transplanted to 120-mL plastic vessels containing nutrient solution spiked with 1, 5, 20 or 90 μg/L of each REE, respectively. The plant samples were in contact with the solution through their fine roots. After 1 d of contact, REEs in plant parts (fine roots, fleshy root and leaves) were measured by ICP-MS. The results showed that the concentrations of REEs in nutrient solution decreased for all REE concentration levels; these elements adsorbed quickly onto the fine roots. Concentration ratios of REEs in the fine roots decreased with increasing atomic number, which indicated that they competed for binding sites on roots. In the plant body, almost all of the absorbed REEs were distributed to the fine roots, while only small amounts of REEs were found in leaves. Chemical forms of REEs in the plant would affect their translocation mechanisms.