On the competitive uptake and transport of ions through differentiated root tissues

• We model the uptake of ions in plant roots by forced diffusion and convection.
• The model includes differentiated root tissues with a focus on the Casparian strip.
• The Casparian strip is modelled via ion permeabilities and reflection coefficients.
• Reduced ion permeabilities affect ion concentrations in the pericycle and xylem.
• Higher reflection coefficients affect concentrations in the cortex and endodermis.

We simulate the competitive uptake and transport of a mixed salt system in the differentiated tissues of plant roots. The results are based on a physical model that includes both forced diffusion and convection by the transpiration stream. The influence of the Casparian strip on regulating apoplastic flow, the focus of the paper, is modelled by varying ion diffusive permeabilities, hydraulic reflection coefficients and water permeability for transport across the endodermis–pericycle interface. We find that reducing diffusive permeabilities leads to significantly altered ion concentration profiles in the pericycle and vascular cylinder regions, while increased convective reflectivities affect predominantly ion concentrations in the cortex and endodermis tissues. The self-consistent electric field arising from ion separation is a major influence on predicted ion fluxes and accumulation rates.

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