Evaluation of leaf water status by means of permittivity at terahertz frequencies

Abstract

We present an electromagnetic model of plant leaves which describes their permittivity at terahertz frequencies. The complex permittivity is investigated as a function of the water content of the leaf. Our measurements on coffee leaves (Coffea arabica L.) demonstrate that the dielectric material parameters can be employed to determine the leaf water status and, therefore, to monitor drought stress in plant leaves. The electromagnetic model consists of an effective medium theory, which is implemented by a third order extension of the Landau, Lifshitz, Looyenga model. The influence of scattering becomes important at higher frequencies and is modeled by a Rayleigh roughness factor.

Monitoring Plant Drought Stress Response Using Terahertz Time-Domain Spectroscopy

“…Yet, these setups are limited in experimental design (Jördens et al, 2009;Castro-Camus et al, 2013). Here, we present a setup suitable for a broad range of applications in ecophysiology and genetics.…”

“…Despite its promising applicability in plant sciences, until now this relatively novel method relied exclusively on measurement setups that allowed only a single measurement per alternating plant (Hadjiloucas et al, 1999;Jördens et al, 2009;Breitenstein et al, 2012;Castro-Camus et al, 2013;Gente et al, 2013). For the purpose of continuously monitoring multiple plants, these setups are only of limited use, since the plants must be relocated for every measurement.…”

Applications of Effective Medium Theories in the Terahertz Regime

“…Different algorithms for the data analysis were developed. Most recently a new approaches, which enables the simultaneous identification of the refractive index n, the absorption coefficient alpha and the sample thickness even in case of ultra thin samples in the sub 100 µm regime has been proposed (Scheller et al 2009, b). As this approach was employed for the material parameter extraction of most datasets presented in this chapter we shall now briefly review its basic working principle.…”

“…If only the majority of the fibres are orientated along the mold flow direction, the resulting birefringence will derivate from the maximum values. As a consequence, THz measurements can be utilized to determine the fibres content of the mixture and their degree of orientation simultaneously (Jördens et al, 2009, b).…”

Espectroscopía Ultrasónica Resonante Sin Contacto y su Aplicación al Estudio de Tejidos Vegetales en Estructura Multicapa = Non-Contact Resonant Ultrasound Spectroscopy and its Application to Study Multilayered Vegetal Tissues

“…In this sense, lower electromagnetic frequency ranges have also been tested (Jördens et al 2009). Martínez et al (1995 described a time domain reflectometry method to estimate leaf disk water status by measuring reflectivity on the X-band (7)(8)(9)(10)(11)(12) with a non-portable laboratory equipment.…”