Role of phase angle measurement in electrical impedance spectroscopy

Abstract

A b s t r a c t. Importance of phase angle measurement during the application of electrical impedance spectroscopy was studied by executing pot experiments with maize. Electrical impedance, phase angle (strength of capacitive character), and dissipation factor in the plant-soil system were scanned between 100 and 10 000 Hz current frequency. The frequency-dependent change in the phase angle could be described by optimum curves culminating within 920-3 650 Hz. Since the rate of energy dissipation is independent of root extent, the higher phase angle and lower energy dissipation were associated with the higher coefficient of determination achieved for the root electrical impedance -root system size (root dry mass and root surface area) regressions. The characteristic frequency selected on the basis of phase angle spectra provided a higher significance level at statistical comparison of plant groups subjected to stress conditions influencing root development. Due to the physicochemical changes observable in aging root tissue, the apex of phase angle spectra, thus the characteristic frequency, shifted continuously toward the higher frequencies over time. Consequently, the regularly repeated phase angle measurement is advisable in time-course studies for effective application of the electrical impedance method, and the systematic operation at the same frequency without determination of phase angle spectra should be avoided.K e y w o r d s: dissipation factor, root capacitance, electrical impedance spectroscopy, phase angle, root surface area INTRODUCTIONDestructive root investigation methods, such as soil cores, in-growth cores, or monoliths are unsuitable for continuous monitoring of root development or activity in response to changing environmental conditions. The applicability of the non-destructive ground penetrating radar, radioactive tracers, MRI or X-ray imaging techniques is also strongly limited in many cases: providing little resolution of root structure (detect clearly coarse roots only), these methods are not adapted for quantification of root surface area and examination of many plant phenomena related to root development (Cao et al., 2010;Èermák et al., 2006). 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 hydro...

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

“…Root tissues undergo characteristic physicochemical changes during plant ontogeny, thus the continuously changing current path and root dielectric properties (eg relative permittivity) leads to an alteration in the computed parameters of the applied regression equation (Cseresnyés et al, 2013a;Dalton, 1995;Ellis et al, 2013). Apart from this limitation, our findings indicate the potential of root EC measurement for in situ monitoring of phenology-dependent changes of plant transpiration and, subsequently, water uptake activity.…”

“…It is important to emphasize that measurement data are comparable only among plants of the same species, grown in the same substrate at the same moisture level in the same time frame (Chloupek et al, 2010). Due to its versatile adaptability, EC measurement can be reliably applicable in various fields of basic and applied plant physiology, ecopysiological and agricultural researches, substituting at least partially the intrusive and labour intensive techniques Cao et al, 2010;Cseresnyés et al, 2012Cseresnyés et al, , 2013aSvačina et al, 2014). CONCLUSIONS 1.…”

Application of electrical capacitance measurement for in situ monitoring of competitive interactions between maize and weed plants

“…By applying the EC method, not only the final outcome of plant interactions can be detected, but it is possible to obtain information about how the competitive growth inhibition be realized in time (decrease in root EC became significant 3-5 days before the appearance of nutrient deficiency symptoms). Competition experiments with EC measurements can be carried out by Temporal changes in the magnitude and phase angle (Ф) of EC in maize refer to the altering functionality and physicochemical structure of the root system (Rajkai et al, 2005;Cseresnyés et al, 2013a). Both parameters increased continually to a maximum, thereafter showed a downward trend (Fig.…”

“…The volumetric water content was measured with a TDR instrument (Trime FM3) then it was adjusted precisely to field capacity. A six-week (42 DAP) duration of experiment since sowing was chosen, firstly because the reliability of EC method is the greatest during the early vegetative stage of plant ontogeny (Cseresnyés et al, 2013a;Ellis et al, 2013b). Secondly, this time practically …”

“…The root-soil system is a relatively poor capacitor. The phase angle is -90° in ideal capacitors irrespective of current frequency, but in the root-soil systems, Ф is much lower in general; furthermore, it depends on the applied current frequency and also on soil properties and plant age Cseresnyés et al, 2013a). Phase angle is the dielectric component of the plasma membrane, and is basically determined by the physicochemical structure of the root tissue.…”