Modeling effective Electrical properties of soil-root continuum to discriminate root traits

Electrical Impedance Tomography is a promising tool for the non-invasive investigation of soil-root systems with potential for phenotype characterization by exploiting the electrical conduction and polarization properties of the soil-root continuum. We performed finite-element modeling of these properties in terms of complex electrical conductivity for a series of simulated root systems, with explicit representation of the root architecture in the finite-element mesh, to understand whether the root systems can be characterized using their effective electrical properties. For the modeling, typical complex conductivity spectra were assumed for the soil, while the spectra of the root segments were taken from frequency-dependent laboratory measurements on maize, differentiating between cortex and stele. Effective properties and anisotropy were examined for different synthetic root architectures generated by Crootbox (a root system architectural model). We relate parameters describing the modeled electrical anisotropy to parameters describing the geometrical anisotropy of the given root structure and discuss different definitions of such parameters, including the ratio of averaged slopes of root segments in two perpendicular directions, the ratio of correlation lengths inferred from variograms of root length density, and others. Our modeling results provide insight into the relation between geometry of the root network and effective electrical properties of the soil-root continuum, and its dependence on the soil-root electrical conductivity contrast, which is very important for the monitoring and characterization of the rooted zone using electrical methods.