Origin, Development, and Applications of Air-Coupled Broadband Ultrasounds for the Study of Tissues and Water Relations in Plant Leaves: A Review

This paper reviews the origin, development and use of air-coupled ultrasonic techniques for the study of plant leaf tissues and their water relations. The two techniques proposed so far are included: Non-Contact Resonant Ultrasound Spectroscopy and Non-Resonant Time Domain Transmittance. While both are completely non-invasive, non-destructive and fast, the former has been used to determine water potential, turgor loss point and differential behavior of various leaf tissues, and has been extensively tested for different species, both in vivo and ex vivo in parallel with in-field experiments; while the latter has recently been proposed as a universal technique that can be applied to plant leaves regardless of the possibility of exciting thickness resonances.