Germanium (Ge) and rare earth element (REE) accumulation in selected energy crops cultivated on two different soils

• Plant species for a phytomining of Ge and REEs were proposed.
• Grasses seem to be most suitable for a phytomining of Ge.
• Contents of P and Fe in shoots correlated significantly with that of REEs.
• Effects of soil properties on the plant availability of Ge and REEs are discussed.

Accumulation of germanium (Ge) and rare earth elements (REEs) in shoots among the functional groups of nine selected energy crops were investigated in a semi-controlled lysimeter experiment. Five species belonging to the functional group of grasses (Hordeum vulgare, Zea mays, Avena sativa, Panicum miliaceum and Phalaris arundinacea) and four species from the group of herbs (Lupinus albus, Lupinus angustifolius, Fagopyrum esculentum and Brassica napus) were cultivated in parallel on two soils with slightly alkaline (pH = 7.8) and slightly acidic (pH = 6.6) conditions. After harvest, concentrations of Ge, La, Nd, Gd, Er, P, Fe, Mn and Si in shoot tissues were determined with ICP-MS. Concentrations of Ge were significantly higher in grasses than in herbs. Conversely, concentrations of La and Nd were significantly higher in herbs than in grasses. Highest concentrations were measured in B. napus (REEs) and Z. mays (Ge). Concentrations of Ge significantly positively correlated with that of Si in the shoots showing low concentrations in herbs and high concentrations in grasses, indicating a common mechanism during the uptake in grasses. Concentrations of REEs correlated significantly positively with that of Fe and P. Cultivation of species on the slightly acidic soil significantly increased the uptake Ge in L. albus and P. arundinacea and the uptake of La and Nd in all species except of P. arundinacea. Our results clearly show that species from the group of grasses are most suitable for a phytomining of Ge. Species with efficient mechanisms for the mobilization of P and Fe in the rhizosphere seem to be most suitable for a phytomining of REEs.