Electrical capacitance of roots in relation to plant electrodes, measuring frequency and root media

Abstract

The electrical capacitance method was applied for the examination of living root systems in a pot experiment. The measured root capacitances gave an unambiguous indication of the development of root mass and length. The root capacitances measured using needle and clamp plant electrodes were closely similar when the roots of whole plants were placed in water, while increasing differences were observed with a decrease in soil water saturation. The difference in capacitance between the plant electrodes is outlined by interpreting the action mechanism of the clamp electrode. The capacitance and electrical impedance spectra (30 Hz-1 MHz) were determined for roots in soil, for pieces of roots washed free of soil, and for the soil itself. The root capacitance was smaller than that of the soil and higher than that of root pieces at 1 kHz, while the capacitance of the soil became equal to that of roots in soil at about 2 kHz. This calls attention to the importance of the measuring frequency when determining root capacitance. A capacitor model with two dielectric media is proposed besides Dalton's model in order to interpret the behaviour of root and soil capacitances. However, its validity requires further verification.