Developing suitable methods for effective characterization of electrical properties of root segments

Developing suitable methods for effective characterization of electrical
properties of root segments
Solomon Ehosioke (1), Maxime Phalempin (2), Sarah Garré (3), Andreas Kemna (4), Sander Huisman (5),
Mathieu Javaux (2), and Frédéric Nguyen (1)
(1) Department of Architecture, Geology, Environment & Constructions, university of Liege, Liège, Belgium, (2) Earth and
Life Institute, Environmental Science, Université catholique de Louvain, Louvain-la-Neuve, Belgium, (3) Biosystems
Engineering Department, Gembloux Agro-Bio Tech, University of Liege, Gembloux, Belgium, (4) Department of Geophysics,
Steinmann Institute, University of Bonn, Germany, (5) Agrosphere (IBG3), Forschungszentrum Ju¨lich GmbH, Ju¨lich,
Germany
The root system represents the hidden half of the plant which plays a key role in food production and therefore
needs to be well understood. Root system characterization has been a great challenge because the roots are buried in
the soil. This coupled with the subsurface heterogeneity and the transient nature of the biogeochemical processes
that occur in the root zone makes it difficult to access and monitor the root system over time. The traditional
method of point sampling (root excavation, monoliths, minirhizotron etc.) for root investigation does not account
for the transient nature and spatial variability of the root zone, and it often disturbs the natural system under
investigation. The quest to overcome these challenges has led to an increase in the application of geophysical
methods. Recent studies have shown a correlation between bulk electrical resistivity and root mass density, but an
understanding of the contribution of the individual segments of the root system to that bulk signal is still missing.
This study is an attempt to understand the electrical properties of roots at the segment scale (1-5cm) for more
effective characterization of electrical signal of the full root architecture. The target plants were grown in three
different media (pot soil, hydroponics and a mixture of sand, perlite and vermiculite). Resistance measurements
were carried out on a single segment of each study plant using a voltmeter while the diameter was measured using
a digital calliper. The axial resistance was calculated using the measured resistance and the geometric parameters.
This procedure was repeated for each plant replica over a period of 75 days which enabled us to study the effects
of age, growth media, diameter and length on the electrical response of the root segments of the selected plants.
The growth medium was found to have a significant effect on the root electrical response, while the effect of root
diameter on their electrical response was found to vary among the plants. More work is still required to further
validate these results and also to develop better systems to study the electrical behaviour of root segments. Findings
from our review entitled “an overview of the geophysical approach to root investigation”, suggest that SIP and EIT
geophysical methods could be very useful for root investigations, thus more work is in progress to develop these
systems for assessing the root electrical response at various scales.