Modification of the tree root electrical capacitance method under laboratory conditions

Abstract

For many years, scientists have been searching for nondestructive methods for the measurement of plant root system parameters. The measurement of electrical capacitance (EC) across the root has been proposed as one such nondestructive method. This article presents a study on the determination of relationships between EC measurement and the shape and size of the electrodes immersed in medium that are used for measurement. Measurement of EC and the parameters characterizing root systems of 1-year-old seedlings of the common beech Fagus sylvatica L. was conducted under laboratory conditions. The measurements of EC were performed between seedling root systems and two different electrodes in the form of a cylinder or a rectangular plate. Statistically significant correlations were found between the capacitance and root system parameters in both the variants; however, the correlations were higher in the case of the flat rectangular plate. Correlation coefficient (r) between EC and total root length was 0.688 for cylindrical electrode and 0.802 for rectangular plate, for total root area 0.641 and 0.818, and for dry weight of root system 0.502 and 0.747. The best-fitted linear regression relationships between the EC and the measured parameters were characterized by low determination coefficients in variants with cylindrical electrodes, and higher with flat rectangular plate electrodes. The results indicated that a two-dielectric media concept is a better model than Dalton's model when attempting to interpret the behavior of root and soil capacitance. The different electrodes probably allow root capacitance measurements to be interpreted from different aspects. However, this hypothesis requires further verification.

Does electrical capacitance represent roots in the soil?

“…The remaining capacitance is thought to be due to the polarization of the epidermal membranes in the root neck and the stem base. The two-dielectric capacitor model assumes that if the soil capacitance is substantially higher than the root capacitance, C R is basically determined by the root system (Rajkai et al 2005;Dietrich et al 2012;Kormanek et al 2016). In the present study, C Soil for the wet substrate proved to be much higher than C R , which met the criteria of this model.…”

“…Likely due to similar reasons, root studies in oilseed plants and young trees showed diurnal patterns in spectral polarization signatures (Weigand and Kemna 2019) and in the magnitude of C R (Ellis et al 2013b). Kormanek et al (2016) found a closer correlation between C R and root size parameters for beech seedlings immersed in hydroponic solution when the root systems were flattened between two flat-plate electrodes and then when the roots were freely arranged inside a cylindrical electrode.…”

“…The C R value detected between the ground and plant electrodes was significantly correlated with the root dry mass (RDM), root length, and surface area (Chloupek et al 2010). The in situ technique provided reliable estimates of the whole root system size (RSS) or the absorptive root surface area for both pot-and field-grown herbaceous plants and tree saplings (Kormanek et al 2016;Postic and Doussan 2016;Cseresnyés et al 2018). However, as C R is very sensitive to soil texture and composition, soil water content (SWC), and electrode protocol, data are only comparable for the same species when grown and measured under the same conditions (Chloupek et al 2010).…”

Field phenotyping of plant roots by electrical capacitance – a standardized methodological protocol for application in plant breeding: a Review

“…13. The construction of the electrodes influences the electrical capacitance values of the roots (Kormanek et al, 2016). In order to evaluate the differences within a single measurement, only the values from one set of electrodes need to be used to perform the root system measurements.…”

Electrical capacitance as a predictor of root dry weight in shrub willow (Salix; Salicaceae) parents and progeny

“…For decades, electrical capacitance has been used to estimate the aboveground biomass of herbaceous perennials (Currie et al, 1987) and forest plantations (Lekas et al, 1990), but few root electrical capacitance (REC) studies have focused on clonal woody perennial plants as a model for predicting root biomass. Previous work on the estimation of root biomass using the REC method has primarily focused on hydroponically grown seedlings (Rajkai et al, 2005; Repo et al, 2005; Cao et al, 2011; Dietrich et al, 2012; Cseresnyés et al, 2013; Kormanek and Tomasz, 2015) or a limited number of genotypes (Whitlow et al, 1992; Pitre et al, 2010).…”