Ultrasonic acoustic emissions in drought-stressed trees - more than signals from cavitation?

Publication Type:Journal Article
Year of Publication:2008
Authors:Zweifel, Zeugin
Journal:New Phytologist
Pagination:1070 - 1079
Date Published:Jan-09-2008
Keywords:cavitation, drought stress, embolism, tree water deficit, ultrasonicacoustic emission
  • 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 (ΔW).
  • Within a low‐dB range (27 ± 1 dB), UAE regularly increased and decreased in a diurnal rhythm in parallel with ΔW 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 ΔW and low‐dB UAE.
BioAcoustica ID: 
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith