Dynamics of Bioelectric Potential in the Root Zone of Plants during Irrigation

Abstract

The paper concerns influence of water distribution on the bioelectric potential in the soil–plant system. Two methods for measuring bioelectric potentials (BEPs) of plants have been compared, namely an invasive installation of needle electrodes (a) and a noninvasive method of providing contact due to root intergrowth through a metal grid (b). It has been shown that needle electrode installation into plant tissue leads to a decrease in the biopotential difference from 70 mV to a noise level within ~ 30 minutes; in fact, this means measuring the potentials generated by the plant organism due to the stress caused by the damage. On the contrary, noninvasive electrode installation provides long-term measurements for months and even longer. A specific system is suggested for automated electrophytogram based on the noninvasive method. It allows one long-term measurement of the plant electrophysiological signal directly under normal living conditions for the rhizosphere; it indicates the current functional state of a plant. An equivalent BEP measurement scheme has been proposed accounting for both electrical properties of the plant and root–inhabited medium. BEPs have been measured under conditions of varying water content in the root zone and water movement along and against the root growth direction. The biopotential is constant on average and fluctuates stochastically in the range from 245 to 275 mV at 60–70% of the total water capacity of the soil substrate. The bioelectric potential decreases almost twice when the soil dries. It is restored after irrigation and the restoration delay time increases with increasing water-deficit period. A model is proposed describing the effects in the system during a water-deficiency regime and irrigation.