Ultrasound pulse emission spectroscopy method to characterize xylem vessels in plant stems

Abstract Although it is well known that plants emit acoustic pulses under drought stress, the exact origin of the waveform of these ultrasound pulses has remained elusive. Here we present evidence for a correlation between the characteristics of the waveform of these pulses and the dimensions of xylem vessels in plants. Using a model that relates the resonant vibrations of a vessel to its dimension and viscoelasticity, we extract the xylem radii from the waveforms of ultrasound pulses and show that these are correlated and in good agreement with optical microscopy. We demonstrate the versatility of the method by applying it to shoots of ten different vascular plant species. In particular, for Hydrangea quercifolia, we further extract vessel element lengths with our model and compare them with scanning electron cryo-microscopy. The ultrasonic, non-invasive characterization of internal vessel dimensions enables a breakthrough in speed and accuracy in plant phenotyping and stress-detection.