Electrical measurement of the absorption surfaces of tree roots by the earth impedance method: 1. Theory

Abstract

Analysis of plant root systems is difficult under field conditions, especially root systems of adult trees, which are large and complex and include fine absorbing roots as well as conducting coarse roots. Although coarse roots can be visualized by several methods, there are technical difficulties with root quantification. The method presented here focuses on the quantification of absorbing root surfaces through an electrical (the modified earth impedance) method. It is based on the experimentally verified fact that an applied electric current flows from the roots to the soil (or vice versa) through the same interfacial areas and predominantly in the same way as water (water solution of minerals or nutrients) flows from the soil to the tree. Based on the different conductivities of tree tissues and soil, the interfacial area, which represents the absorbing root surfaces (or root absorption zones), can be calculated. Only the theoretical description of the method is presented in this paper: the experimental verification of the method under field conditions is presented in the accompanying paper.

Above- and below-ground tree parameters and their development after modelling of thinning in young elm stands

“…The ARA was measured by the modified earth impedance (MEI) method using the four-electrode system developed by Staněk (1997) and Aubrecht et al (2006). This system has been field-tested by Čermák et al (2006, 2013a, 2013b), Butler et al (2010), Urban et al (2011) and others.…”

“…The point at which the drop in voltage plateaus is considered to be l, which corresponds to the mean distance of all the absorbing root segments of the tree. Resistivity of the water -conducting tissue (ρ wood ) of the roots was calculated using the four-point Wenner method where ρ wood = 2πaR (Aubrecht et al, 2006). The four electrodes were inserted into the sapwood at equal distances.…”

“…The significance of the RAI:LAI ratio was previously noted by Čermák and Prax (2001), but procedures for the empirical measurement of ARA were not developed until later (Aubrecht et al, 2006). The estimation of RAI (i.e.…”

“…One of the fundamental parameters of trees is the active ion absorptive root area, a parameter that is comparable to leaf area. The absorptive root area can be measured using the modified earth impedance method, which was developed for this purpose (Staněk, 1997;Aubrecht et al, 2006). Measurement of the absorptive root area index (RAI) is important for characterising the capacity of roots to absorb and conduct water (Čermák et al, 2013a) and provides a way of characterising ecosystem functioning as a physiologically meaningful index of the below-ground absorbing area (Butler et al, 2010).…”

Simultaneous monitoring of electrical capacitance and water uptake activity of plant root system

“…Crops were observed to show characteristic changes in the root/shoot ratio during their ontogeny, as well as to produce varietal differences in root characteristics, water extraction and water use (Siddique et al, 1990). As root conductivity and permeability are reliable indicators for water uptake activity and absorptive root surface area (Aston and Lawlor, 1979;Aubrecht et al, 2006), we hypothesised that phenological changes and differences in root water uptake (measured indirectly through the transpiration water loss) could be monitored by EC measurement carried out repeatedly during plant ontogeny. Since arbuscular mycorrhizal fungal (AMF) colonization is known to alter root morphology, conductivity and water uptake capacity, and thus subsequently electrical root properties (Augé, 2001;Cseresnyés et al, 2013b), AMF-infected and non-AMF plants were also used for the experiments.…”