Journal
JOURNAL OF EXPERIMENTAL BOTANY
Volume 62, Issue 6, Pages 1857-1869Publisher
OXFORD UNIV PRESS
DOI: 10.1093/jxb/erq370
Keywords
Absorbing root surface area; conductance; electrical resistance; tree capacitance
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Funding
- Flanders-Czech bilateral scientific cooperation [BWS BOF 2006]
- foundation of the Mendel University Brno [IGA 9/2008, IGA 12/2010]
- EEA [A/CZ0046/2/0009]
- Czech Science Foundation [GA526/08/1050]
- Federal Environment Agency of Switzerland (BAFU)
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Several electrical methods have been introduced as non-invasive techniques to overcome the limited accessibility to root systems. Among them, the earth impedance method (EIM) represents the most recent development. Applying an electrical field between a cormus and the rooted soil, the EIM measures the absorptive root surface area (ARSA) from grounding resistance patterns. Allometric relationships suggested that this method was a valuable tool. Crucial assumptions for the applicability of the EIM, however, have not been tested experimentally. Focusing on tree root systems, the present study assesses the applicability of the EIM. Six hypotheses, deduced from the EIM approach, were tested in several experiments and the results were compared with conventional methods. None of the hypotheses could be verified and the results allow two major conclusions. First, in terms of an analogue electrical circuit, a tree-root-soil continuum appears as a serial circuit with xylem and soil resistance being the dominant components. Allometric variation in contact resistance, with the latter being the proxy for root surface area, are thus overruled by the spatial and seasonal variation of soil and xylem resistances. Second, in a tree-root-soil continuum, distal roots conduct only a negligible portion of the electric charge. Most of charge carriers leave the root system in the proximal parts of the root-soil interface.
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