Ultrasonic acoustic emissions in drought-stressed trees--more than signals from cavitation?
Ultrasonic acoustic emission (UAE) in trees is often related to collapsing water columns in the flow path as a result of tensions that are too strong (cavitation). However, in a decibel (dB) range below that associated with cavitation, a close relationship was found between UAE intensities and stem radius changes. UAE was continuously recorded on the stems of mature field-grown trees of Scots pine (Pinus sylvestris) and pubescent oak (Quercus pubescens) at a dry inner-Alpine site in Switzerland over two seasons. The averaged 20-Hz records were related to microclimatic conditions in air and soil, sap-flow rates and stem-radius fluctuations detrended for growth (Delta W). Within a low-dB range (27 +/- 1 dB), UAE regularly increased and decreased in a diurnal rhythm in parallel with DeltaW on cloudy days and at night. These low-dB emissions were interrupted by UAE abruptly switching between the low-dB range and a high-dB range (36 +/- 1 dB) on clear, sunny days, corresponding to the widely supported interpretation of UAE as sound from cavitations. It is hypothesized that the low-dB signals in drought-stressed trees are caused by respiration and/or cambial growth as these physiological activities are tissue water-content dependent and have been shown to produce courses of CO(2) efflux similar to our courses of Delta W and low-dB UAE.
Zweifel
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Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Zürcherstrasse 111, CH-8903 Birmensdorf, Switzerland.|Institute of Plant Sciences, University of Bern, Altenbergrain 21, CH-3013 Bern, Switzerland.
Zeugin
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F
ETH Zurich, Institute of Plant Sciences, Universitätsstrasse 2, CH-8092 Zurich, Switzerland.|Institute of Plant Sciences, University of Bern, Altenbergrain 21, CH-3013 Bern, Switzerland.
D001692:Biological Transport; D001696:Biomechanical Phenomena; D002940:Circadian Rhythm; D003681:Dehydration; D041605:Pinus sylvestris / Q000378:metabolism / Q000502:physiology; D029963:Quercus / Q000378:metabolism / Q000502:physiology; D014197:Trees / Q000378:metabolism / Q000502:physiology*; D014465:Ultrasonics; D014867:Water / Q000378:metabolism; D052584:Xylem / Q000378:metabolism / Q000502:physiology
D014867:Water