Electrical Capacitance as the Indicator of Root Size and Activity

Abstract

A new method is introduced to agricultural practice for measuring the living active root of the plants. The measured root capacitance is interpreted in electro-chemical principles. In addition to the electrochemical interpretation of the measurements we aimed to find a non-wounding electrode instead of the needle plant electrode. Another reason for dealing with the tweezer plant electrode was to decrease the relatively high standard deviation of the root capacitance readings due to the relatively high uncertainty of hitting the xylem with the needle plant electrode. To improve and standardize the contact between the tweezer plant electrode and the stem a high electrical conductivity gel (UNIGEL) was applied on the stem before clipping the tweezers. Experiments for the root capacitance measurements were made in temperature and light controlled climate chambers (Conviron, Canada) in 2 litre plastic pots filled with 4:1 soil:sand mixture and water culture. Comparison of the root capacitances of five-week old sunflower plants measured with the needle and the tweezer plant electrodes proved identical in water culture and capillary water saturated soil. However, the applicability of the tweezer plant electrode needs further study for other plants and environmental conditions. The effect of measurement frequency on root capacitance and resistance with the HP4284A impedance bridge was also studied to see the effectiveness of polarization (Figure 1). From Figure 1 it can be seen that root capacitance decreased at frequencies above 1 kHz, while it increased up to the dielectric constant of water at lower frequencies. An interpretation of measurable root capacitance in the soil-plant system is given using separate measured plant tissue and soil capacitances. We established that root capacitance in the soil-plant system approximates the capacitance of the root tissue. Good correlation was found between root capacitance and the calculated root surface area (RA) for sunflower plants (Figure 2). The GW LCR-814 was found suitable for making root capacitance measurements. Finally, further experimental work is needed to collect information for the more general and extended applicability of the method before it becomes a routine tool in ecological and agricultural practice.

Analysis of Root Growth by Impedance Spectroscopy (EIS)

“…The second component is the soil-root interface as described by Dalton (1995) and Rajkai et al (2002). This interface includes the root surface membrane and the rhizosphere.…”

Role of phase angle measurement in electrical impedance spectroscopy

“…Conversely, electrical impedance (EI) and electrical capacitance (EC) measurements in a plant-soil system offer good opportunities of rapid in situ investigation of the root system size and root activity without any intrusion into plant life function. By fixing an electrode at the plant stem and embedding the other one in the soil and connecting them by an LCR-instrument, the measured root EI and EC are directly correlated with root mass, root length, or root surface area (Chloupek, 1972;Ozier-Lafontaine and Bajazet, 2005;Rajkai et al, 2002). EI and EC methods have been used for investigation of detached plant tissues and organs subjected to various stress conditions (cold acclimation, freeze-thaw injury, drought, nutrient deficiency, or pathogen infection) as well as for studying intact root systems of plants cultivated in soil or grown in hydroponic solution (Chloupek et al, 2006;Cseresnyés et al, 2012Cseresnyés et al, , 2013Preston et al, 2004).…”

Measurement of the tree root growth using electrical impedance spectroscopy

“…Recently new developments in the determination of root mass have been obtained by using electrical capacitance (Dalton 1995, van Beem et al 1998, Ozier-Lafontaine et al 2001, Matsumoto et al 2001, Rajkai et al 2002. The method is based on the assumption that the capacitance of the root/soil-system changes when the contact surface area between roots and the soil increases with growth (Chloupek 1977, Dalton 1995.…”

“…However, more comprehensive information of the root system may be obtained by multi-frequency measurement and by using the approach of Electrical Impedance Spectroscopy (EIS) but this technique has not used to quantify root growth. In a recent study multi-frequency response of capacitance and resistance for sunflower plants was measured but the data was not analyzed in relation to an electric circuit model of the system (Rajkai et al 2002).…”