Article,
Ultrasonic acoustic emissions in drought-stressed trees - more than signals from cavitation?
New Phytologist, 0 (0): ??? (0)
DOI: 10.1111/j.1469-8137.2008.02521.x
Abstract
Summary . 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 de-trended for growth (DeltaW). . 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 CO2 efflux similar to our courses of DeltaW and low-dB UAE. New Phytologist (2008) doi: 10.1111/j.1469-8137.2008.02521.x c The Authors (2008). Journal compilation c New Phytologist (2008)
