The influence of roots on soil's electrical signature

Abstract

Detecting and monitoring roots and their activity in soil is of great importance as it controls water and nutrient transport, soil carbon dynamics, and soil microorganisms. However, roots are hidden in the soil, they are heterogeneous, and dynamics; therefore, in-situ measurements of their properties and the involved processes are highly challenging. The spectral induced polarization (SIP) is a geophysical method that allows noninvasive mapping of subsurface properties and processes. Recently, the quadrature conductivity (measured with the SIP method) was positively correlated with root biomass and root surface area in hydroponics. Unlike the nonpolarized hydroponic solution (at frequencies <1000 Hz, relevant to the SIP method), the soil is a polarizable medium, and various soil-root interactions (e.g., water and nutrient uptake, root exudation, etc.) are expected to influence the soil SIP signature. Therefore, this research aimed to assess the impact of roots on the SIP signature of soil. We conducted a series of experiments in which we measured and monitored the SIP signature of soil in which wheat plants are growing. Supplementary measurements included soil water content, pore water salinity, and root biomass. Our results show that, unlike in hydroponic, there is an inverse relationship between root biomass and quadrature conductivity. Most of the decrease in the quadrature conductivity was associated with the water content decrease. We suggest that the unexplained decline in the quadrature conductivity is associated with various soil-root interactions, such as selective uptake of nutrients and root exudation, but further research is needed.