Abstract
The wide band and air-coupled ultrasonic resonant spectroscopy together with a modified Simulated Annealing metaheuristic algorithm and a 1D layered acoustic-model are used to resolve the structure of plant leaves. In particular, this paper focuses on the extraction of the surface density of the different layers of tissue in leaves having a relatively simple structure. There are three main reasons to select the surface density as the focus of this study: (i) it is a parameter directly extracted by the proposed technique and it requires no further processing, (ii) it is relevant in order to study the dynamic of the water within the different tissues of the leaves and also to study the differential development of the different tissues, and (iii) unlike other parameters provided by this technique (like resonant frequency, impedance, ultrasonic elastic modulus, or ultrasonic damping), this parameter can be easier to understand as it is a direct measure of mass per unit surface. The selection of leaves with a simple structure is justified by the convenience of avoiding an unnecessary complication of the data extraction step. In this work, the technique was applied to determine the surface density of the palisade and spongy parenchyma layers of tissue of Ligustrum lucidum, Vitis vinifera, and Viburnum tinus leaves. The first species was used to study the variation of the surface density at full turgor with the thickness of the leaf, while the two other species were used to study the variation of the surface densities with the variation in the leaf relative water content. Consistency of the results with other conventional measurements (like overall surface density, and cross-section optical and cryo-SEM images) is discussed. The results obtained reveal the potential of this technique; moreover, the technique presents the additional advantage that can be applied in-vivo as it is completely non-invasive, non-destructive, fast, and equipment required is portable.
Highlights
The wide-band, air-coupled ultrasonic resonant spectroscopy method has been presented by Álvarez-Arenas et al (2018)
This method is an extension of the air-coupled ultrasonic resonant spectroscopy method presented in Álvarez-Arenas et al (2009); Sancho-Knapik et al (2010, 2012, 2013a) that has been widely used for different applications
The two-layered model of L. lucidum, V. tinus and V. vinifera provides a reasonable leaf model approach based on its ability to reproduce all features observed in the ultrasonic leaf resonances and that its consistency with actual leaf structure as revealed by the cryoSEM images
Summary
The wide-band, air-coupled ultrasonic resonant spectroscopy method has been presented by Álvarez-Arenas et al (2018). 2014) where the determination of leaves water content attracted most of the interest: (Álvarez-Arenas et al, 2016; Sancho-Knapik et al, 2016; Farinas et al, 2019) This ultrasonic technique is one of the methods available to measure physical properties of plant leaves. The novel wide band ultrasonic technique present the unique feature that it can obtain information about the different layers in the leaves, in a completely non-invasive and non-destructive way, which allows us to study the overall leaf properties and their variations, and the differences between the main layers of tissue in the leaves and the differences in the variation of their properties (for example with the leaf development or with the modification of the leaf water content)
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