A new method for characterizing the complex electrical properties of root segments

The application of geophysical methods to root investigation is increasing in recent years because of the limitations associated with the use of traditional methods (root excavation, monoliths, minirhizotron etc.). Point sampling is only partially satisfactory as a result of the spatial variability and dynamics of the roots zone. Geophysical methods address these limitations by offering high resolution and non-invasive approaches to root investigation due to their ability to infer properties and structures of the subsurface as well as the flow and transport processes occurring in the shallow subsurface, at various spatial scales. Recent studies (Weigand and Kemna 2017; Mary et al. 2017) have reported a low frequency polarization of root systems and have shown that SIP/EIT holds a promising future for root system characterization. Despite these significant improvements, there is still a knowledge gap regarding the electrical response of fine roots at the segment scale which is essential to enable us to account for the effect of roots in the estimation of soil moisture content of rooted soils or to exploit electromagnetic methods to characterize certain root system characteristics. We hereby propose a method for the characterization of electrical properties of single root segments of various plants resulting from an externally applied electrical field. A sample holder was designed and tested on ideal resistors and root segments, and was found to be suitable for assessing the electrical properties of root segments of 1-5 cm length and 2 mm diameter at a frequency range of 1Hz – 45 KHz. The system was then used to obtain complex electrical responses of the root segments of the target plants in the laboratory. This enabled us to study different root properties and their effects on the root electrical signals. Our results suggest that fine roots could be differentiated from soils because they show lower resistivity and polarizes more than soils.