Natural and laser-induced cavitation in corn stems: On the mechanisms of acoustic emissions

Abstract

Water in plant xylem is often superheated, and therefore in a meta-stable state. Under<br />certain conditions, it may suddenly turn from the liquid to the vapor state. This cavitation<br />process produces acoustic emissions. We report the measurement of ultrasonic acoustic<br />emissions (UAE) produced by natural and induced cavitation in corn stems. We induced<br />cavitation and UAE in vivo, in well controlled and reproducible experiments, by irradiat-<br />ing the bare stem of the plants with a continuous-wave laser beam. By tracing the source<br />of UAE, we were able to detect absorption and frequency ltering of the UAE propagat-<br />ing through the stem. This technique allows the unique possibility of studying localized<br />embolism of plant conduits, and thus to test hypotheses on the hydraulic architecture of<br />plants. Based on our results, we postulate that the source of UAE is a transient cavity<br />oscillation" triggered by the disruptive eect of cavitation inception.