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Based on the differences of lupin and corn in Si requirement and their capacity to release organic acids for P mobilisation both plant species were compared in respect to As mobilisation and plant As uptake and release which is closely linked to P and Si nutrition.Plants were grown with and without P fertilization in an As contaminated floodplain soil in compartment systems which enabled temporally resolved sampling of soil solution with increasing distance from the root surface.Although no direct increase of P or AsV concentration in soil solution could be detected, lupins showed higher P and As uptake but lower root to shoot translocation of As compared to corn plants. Higher root As concentrations in lupins corresponded to higher AsIII concentration in soil solution which increased with time and corresponded to the recently demonstrated diffusion driven efflux of As in the form of AsIII via aquaglycerol channels. It is well established that AsV, the form of As initially present in the floodplain soil, is taken up via P transporters. Hence the higher As uptake of lupin is in line with previous results showing higher P uptake capacity per unit root length for lupin compared to corn. A lower capacity for As efflux in lupin as it was expected due to lower Si requirement of lupin compared to corn could not be demonstrated.

The transfer of nutrients and contaminants from bulk soil to roots and into plants depends on many plant and soil processes. The RhizoMath approach for modeling co-occurring processes in the rhizosphere, including speciation in the soil solution, is based on coupling the mathematical package MATLAB with the geochemical code PHREEQC. In addition to the built-in initialization module that performs calibration against experimental data, RhizoMath's greatest advantage is that different geochemical models (with and without charge balance) and geometries (planar and radial) are already included. Moreover, due to its graphical user interface, the tool can be applied without changing the source code or a complex input file. The model was verified using a benchmark and experimental data: (i) the initialization module was successfully applied to describe concentrations measured in soil solution samples; (ii) the theoretical problem "diffusion of K toward a single root" was used to demonstrate that the performance of applied numerical methods is comparable to other approaches; and (iii) for compartment system experiments involving more complex speciation, RhizoMath was able to describe the observed effects of citrate exudates on the simultaneous transport of arsenate and phosphate that compete for surface binding sites with each other and with other oxyanions such as citrate. [ABSTRACT FROM AUTHOR]