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Abstract: Phytomining is a phytoassisted technique for the extraction of economically valuable elements from soils and offers a promising chance to improve the supply of critical raw materials such as germanium (Ge) and rare earth elements (REEs). The efficiency of phytoextraction depends on numerous soil-associated and plant-associated factors (e.g. concentrations of target elements in potentially plant available soil fractions, rhizosphere processes and uptake mechanisms of plants). The aim of this study was to evaluate the effect of different soil properties (pH, compost amendment) on the mobility of selected target elements for phytoremediation (As, Pb, Cd, Zn) and phytomining (Ge, REEs) in soil and shoot concentrations in Phalaris arundinacea. Until today, only little is known about the influence of soil-associated factors on the availability of trace elements for Phalaris arundinacea, especially for the target elements Ge and REEs. In a field experiment we cultivated 10 different genotypes of Phalaris arundinacea on four different substrates with similar element concentrations but different pH-values (pH 6.6 – 7.8) and levels of compost amendment (5l /m2 compost or without compost). On each of the substrates we cultivated Phalaris arundinacea (genotypes) with two replicates on plots 4 m2 each and installed suction cups to collect soil solution. After harvest concentrations of Ge, REEs, P, Fe, Mn, Zn, Pb, As and Cd in shoots and soil solution were determined with ICP-MS. Compared to the slight alkaline soil, acidic soil conditions significantly increased shoot concentrations of Fe, Mn, As, Cd, Pb and REEs. Under acidic soil conditions addition of compost further increased the concentrations of all investigated target elements in shoots of P. arundinacea except of As. In soil solution only concentrations of Fe and Mn significantly increased due to the compost amendment, while concentrations of P, Ge, REEs, Cd and Pb decreased. Lower concentrations of elements in soil solution may result from increased adsorption of the elements onto soil particles (in case of P and Ge) or the uptake of the elements by plants (in case of Cd and Pb). We conclude that amendment of soil with compost seems to be a sustainable approach to enhance the uptake of plant nutrients such as Fe and Mn as well as REEs into shoots of Phalaris arundinacea and to reduce the mobility of potential toxic trace elements (Cd, Pb) in soil solution.

Keyword: Germanium, rare earth elements, heavy metals, phytomining, phytoremediation, Phalaris arundinacea, soil solution