Substituting Stem's Water Content by Electrical Conductivity for Monitoring Water Status Changes

Rapid and sensitive detection of stress in trees due to irrigation practices, draught, salinity, pollution, lack of nutrients, or diseases may be useful for research and practical purposes. Tree stress could be monitored by following changes in wood water content via time domain reflectometry (TDR). We have searched for a user-friendly and less expensive tool because, although TDR is perhaps the most suitable method, it is too expensive and complicated for everyday use. The objective of this study was to understand the relations between the electrical conductivity (σ stem ) and water content (θ stem ) in tree stem segments of seven species with TDR probes installed. By leaching stem segments with salt solutions or air we were able to change the salinity and water content independently. We have shown that (i) σ stem is more sensitive to changes in θ stem than to changes in salinity of the sap, and (ii) 30-mm-long rods on the TDR probe can sensitively and accurately measure θ stem . We propose that σ stem changes might be used as a proxy for changes in stem water content or stem water potential. Hence, electrical resistivity measurements may substitute for water content measurements with the following advantages: improved accuracy, higher flexibility in probe construction, application to stem diameters <30 mm, and significantly lower costs.

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