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Fig. S1 Amount of inline image held on the soil's solid phase as a function of solution inline image concentration.

Fig.S2 Total amount of inline image present in soil solution and held on the soil's cation exchange phase in Triticum aestivum planted and unplanted microcosms.

Fig. S3 Time-dependent mineralization of 14C-labelled glutamate in soil in the presence and absence of wheat (Triticum aestivum) roots.

Fig. S4 NanoSIMS imaging and analysis of wheat (Triticum aestivum) roots in situ within the embedded soil core after exposure to 15N-labelled glutamate uptake.

Fig. S5 Influence of external solution glutamate concentration on the growth rate of wheat (Triticum aestivum) roots exposed to various concentrations of glutamate.