Coupling reactive transport processes with root system architecture and functions: principles and application examples.

We developed a novel soil-plant interaction model based on the coupling of a root system architecture model (ArchiSimple) with a reactive transport model (Min3P). The main novelty of this macro-scale model is to facilitate the simulation of soil-plant interactions by simultaneously accounting for principles of plant biology, aqueous geochemistry and the transport of water, solutes and gases in soil. This contribution is devoted to introduce the formulation of the coupled soil-plant interaction model and to present two application examples highlighting the capabilities of this tool for tackling a wide range of agronomic and environmental issues. The first application focuses on phosphorus acquisition by annual plants from alkaline soils. In this case, we performed 2D simulations to investigate the role of common root processes (i.e., nutrient uptake and related pH changes) in releasing phosphate from the mineral and adsorbed pools in soil. Results are compared with observed data collected in the field and in the laboratory published in the literature . The second application is addressing the capacity of select plant species to induce the formation of calcium carbonates (and alkalization) in tropical soils through the oxalate-carbonate pathway (OCP). We simulate OCP for Iroko trees (Milicia excelsa), because these plants were shown capable of sequestering substantial amounts of calcium carbonate over the life-span of a tree (80 years) in Ivory Coast. Our process-based modeling investigation provides insight in elemental balances, most importantly the fate of carbonate produced by the decomposition of oxalate, which is not only sequestered in the form of calcium carbona