Frequency Characteristics of AE Caused by Bubble Motion in Plant's Vessels

Abstract

Acoustic emission (AE) can be used to evaluate drought stress (water stress) in plants. Although bubble motion in plant vessels is suspected of being the source of AE generated by plants (burst-type AE), this has not yet been demonstrated experimentally. This study examined whether burst-type AE is caused by bubble motion by comparing the detected frequency with the theoretical frequency estimated based on a bubble motion equation. Four experimental treatments with different soil dry densities and water supply regimes were established, and the effect of the treatment conditions on AE characteristics was clarified. AE induced by water stress was extracted by focusing on the maximum amplitude and the centroid frequency calculated by wavelet transform analysis. The results showed that the measured frequency and the estimated frequency were almost equal, which demonstrates that the model agreed with the actual measurements and that the burst-type AE can be attributed to bubble motion. The AE induced by water stress had a smaller maximum amplitude and a higher centroid frequency than the AE detected during the water supply regime. Therefore, focusing on the centroid frequency may facilitate the extraction of AE induced by water stress.