Electrical characterization of the root system: a noninvasive approach to study plant stress responses

Imre Cseresnyés,Ramóna Kovács,Kálmán Rajkai,Bettina Sepovics,Anna Füzy,Tünde Takács,István Parádi

doi:10.1007/s11738-019-2959-x

Abstract

A pot experiment was designed to demonstrate that the parallel, single-frequency detection of electrical capacitance (CR), impedance phase angle (ΦR), and electrical conductance (GR) in root–substrate systems was an adequate method for monitoring root growth and some aspects of stress response in situ. The wheat cultivars ‘Hombar’ and ‘TC33’ were grown in a rhyolite-vermiculite mixture under control, and low, medium, and high alkaline (Na2CO3) conditions with regular measurement of electrical parameters. The photochemical efficiency (Fv/Fm) and SPAD chlorophyll content were recorded non-intrusively; the green leaf area (GLA), shoot dry mass (SDM), root dry mass (RDM), and root membrane stability index (MSI) were determined after harvest. CR progressively decreased with increasing alkalinity due to impeded root growth. Strong linear CR–RDM relationships (R2 = 0.883–0.940) were obtained for the cultivars. Stress reduced |ΦR|, presumably due to the altered membrane properties and anatomy of the roots, including primarily enhanced lignification. GR was not reduced by alkalinity, implying the increasing symplastic conductivity caused by the higher electrolyte leakage indicated by decreasing root MSI. Fv/Fm, SPAD value, GLA, and SDM showed decreasing trends with increasing alkalinity. Cultivar ‘TC33’ was comparatively sensitive to high alkalinity, as shown by the greater relative decrease in CR, SDM, and RDM under stress, and by the significantly lower MSI and higher (moderately reduced) |ΦR| compared to the values obtained for ‘Hombar’. Electrical root characterization proved to be an efficient non-intrusive technique for studying root growth and stress responses, and for assessing plant stress tolerance in pot experiments.

Highlights

Several technical difficulties limit or restrict the access to root growth and functional parameters in natural soil environments (Milchunas 2012)
The present study aimed to show that the monitoring of electrical parameters, such as capacitance (CR), impedance phase angle (ΦR), and conductance (GR), in intact root–substrate systems at a single low (1 kHz) frequency gives useful insights into some aspects of root development in pot cultures
The stress effect was more pronounced for cultivar T, in which membrane stability index (MSI) was significantly reduced by any salt treatment, while in cultivar H, only high alkalinity induced a significant decline in membrane stability

Summary

Introduction

Several technical difficulties limit or restrict the access to root growth and functional parameters in natural soil environments (Milchunas 2012). In contrast with Dalton’s model, which considers the soil solution as purely conductive, Rajkai et al (2005) and Dietrich et al (2013) highlighted the fact that rooting substrates provide capacitance (CS). They proposed the “two-dielectric capacitor model”, which contains a root and a soil dielectrics connected serially and have different relative permittivities (εr). The present study aimed to show that the monitoring of electrical parameters, such as capacitance (CR), impedance phase angle (ΦR), and conductance (GR), in intact root–substrate systems at a single low (1 kHz) frequency gives useful insights into some aspects of root development in pot cultures. Differences were accepted as significant at P < 0.05

Results

Discussion

Compliance with ethical standards