Plant physiologists have known for several decades that plants produce noises. To a large extent, these sounds are of hydraulic origin, i.e., they are related to the circulation of water as part of plant transpiration. The range of sound emissions extends far beyond the audible range into the ultrasound spectrum.
Their analysis allows statements to be made about the physiology of the plants: for example, when individual water columns in the wood collapse under very dry conditions, ultrasound pulses are generated. These pulses are above the human hearing range and thus not audible for humans.
Aim of the measurements
The aim of the ultrasound measurements is to record previously unmeasurable physiological processes from inside the plant and to show correlations with atmospheric conditions, day and night rhythm, light conditions, and the water present in the tree.
The measurement of sound waves in the ultrasonic range requires a piezoelectric sensor, a signal amplifier and an audio interface. A correct coordination between these three components is essential to produce reliable sound data.