Determination of plant leaves water status using air-coupled ultrasounds

Water in plants is studied by analyzing the magnitude and the phase spectra of the first thickness resonance of their leaves. These resonances appear at ultrasonic frequencies and have been excited and sensed using air-coupled ultrasounds. In spite of the complex leaf microstructure, the resonances of the leaves can be well described by the resonances of either a homogeneous and isotropic solid plate or a four-layered composite. Results reveal that these resonances are strongly sensitive to leaf microstructure, water content and water status in the leaf. As the technique is completely non-contact and non-invasive, it offers a unique possibility to study the complex dynamic behaviour of water in plants and the water exchange between the plant and the atmosphere across the leaves.