Metallophores are chelating ligands exuded by plants and microorganisms for trace metal acquisition, particularly under conditions of low trace metal availability in their external environment. They increase trace metal solubility by forming soluble metal-metallophore complexes, which can be transported towards the exuding organism by advective or diffusive transport, hence facilitating the uptake of the target metal. However, in natural environments, processes occur that compromise the efficiency of metallophore promoted trace metal acquisitions, e.g., adsorption of metallophores and metal-metallophore complexes, degradation of metallophores, and competitive complexation of non-target metals. The impact of such processes on metallophore-mediated trace metal acquisition can be quantitatively assessed with geochemical models.<br/>It will be shown and discussed that metallophore equilibrium speciation in soil solution can be predicted through multi-surface modelling using the computer program ECOSAT. In the presented multi-surface approach, sorption models (NICA-Donnan, CD-MUSIC, Donnan model, DDL) are combined assuming linear additivity, to calculate metal activities as well as the distribution of metals over soil reactive compounds and the metallophore. Model predictions will be compared with experimental data and the validity of the equilibrium assumption will be discussed.<br/>For including dynamic processes, e.g. exudation and transport, thermodynamic models can be combined with kinetic transport models. A pseudo-2D model was composed in Orchestra to describe the rhizosphere concentration of the metallophore DMA as a function of time. DMA is exuded by grass species in a diurnal pulse release for a few hours each day. After release, DMA engages in rhizosphere processes that affect its soluble concentration. Processes that have been incorporated into the model include exudation, diffusive transport, adsorption, ligand degradation, etc. Results from model simulations will be presented and will be discussed in the context of Fe acquisition.

Modelling speciation and uptake of trace metal as influenced by metallophores

251st National Meeting (2016)

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