Extending Fluspect to simulate xanthophyll driven leaf reflectance dynamics

Abstract

The xanthophyll cycle regulates the energy flow to photosynthetic reaction centres of plant leaves. Changes in the de-epoxidation state (DEPS) of xanthophyll cycle pigments can be observed as changes in the leaf absorption of light with wavelengths between 500 to 570 nm. These spectral changes can be a good remote sensing indicator of the photosynthetic efficiency, and are traditionally quantified with a twoband physiologically based optical index, the Photochemical Reflectance Index (PRI). In this paper, we present an extension of the plant leaf radiative transfer model Fluspect (Fluspect-CX) that reproduces the spectral changes in a wide band of green reflectance: a radiative transfer analogy to the PRI. The idea of Fluspect-CX is to use in vivo specific absorption coefficients for two extreme states of carotenoids, representing the two extremes of the xanthophyll de-epoxidation, and to describe the intermediate states as a linear mixture of these two states. The 'photochemical reflectance parameter' (Cx) quantifies the relative proportion of the two states. Fluspect-CX simulates leaf chlorophyll fluorescence (ChlF) excitation-emission matrices, as well as reflectance (R) and transmittance (T) spectra as a function of leaf structure, pigment contents and Cx. We describe the calibration of the model and test its performance using various experimental datasets. Furthermore, we retrieved Cx from optical measurements of various datasets. The retrieved Cx correlates well with xanthophyll DEPS (R2=0.57), as well with non-photochemical quenching (NPQ) of fluorescence (R2=0.78). The correlation with NPQ enabled us to incorporate Fluspect-CX in the model SCOPE to scale the processes to the canopy level. Introducing the dynamic green reflectance into a radiative transfer model provides new means to study chlorophyll fluorescence and PRI dynamics on leaf and canopy scales, which is crucial for the remote sensing.

Relation of Photochemical Reflectance Indices Based on Different Wavelengths to the Parameters of Light Reactions in Photosystems I and II in Pea Plants

“…In particular, these correlations are sensitive to illumination conditions and the scale of measurement, as well as to the parameters of stressor-induced changes in photosynthetic processes [37,56]. The use of light-induced changes in PRIs (∆PRIs) can strongly decrease errors of the PRI value; however, correlation coefficients between ∆PRI and photosynthetic parameters can be also varied [31,[57][58][59][60][61][62][63][64].…”

Estimating photosynthetic capacity from leaf reflectance and Chl fluorescence by coupling radiative transfer to a model for photosynthesis

“…We established the link between the radiative transfer model FLUSPECT and the photosynthesis model via parameter g (the absolute ChlF quantum yield) to e = F s /F o , and C x to K n via a calibrated coefficient (Vilfan et al, 2018). This introduces uncertainty, because PAM F s cannot be reproduced well by the model.…”

“…FLUSPECT simulates leaf reflectance q, transmittance s, and ChlF spectra as a function of leaf pigment content and structure. Recently, FLUSPECT has been extended to simulate the dynamics of green q as a function of the xanthophyll de-epoxidation, an RT analogy to the PRI (Vilfan et al, 2018).…”

Decomposing reflectance spectra to track gross primary production in a subalpine evergreen forest

“…PROSPECT+SAIL (PROSAIL, Jacquemoud et al, 2009) is a process-based 1-D canopy radiative transfer model (RTM) that models canopy reflectance, given canopy structure information (SAIL) as well as leaf pigment contents (PROSPECT) (Jacquemoud and Baret, 1990;Vilfan et al, 2018).…”