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Ultrasonic acoustic emissions in drought‐stressed trees – more than signals from cavitation?
Author(s) -
Zweifel R.,
Zeugin F.
Publication year - 2008
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/j.1469-8137.2008.02521.x
Subject(s) - scots pine , environmental science , cavitation , range (aeronautics) , atmospheric sciences , growing season , horticulture , botany , pinus <genus> , biology , materials science , acoustics , geology , physics , composite material
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 (Δ W ). • Within a low‐dB range (27 ± 1 dB), UAE regularly increased and decreased in a diurnal rhythm in parallel with Δ W 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 Δ W and low‐dB UAE.