Abstract
Chlorophyll fluorescence (ChlF) is a useful indicator of plant photosynthesis and stress conditions. ChlF spectra can be simulated with the Fluspect model, which is a radiative transfer model that simulates leaf reflectance, transmittance, and fluorescence; however, it has never been used or validated under natural conditions. In this paper, a new fluorescence quantum yield efficiency of photosystem (FQE) retrieval method based on the Fluspect model is proposed for use in simulating ChlF in two healthy varieties of soybeans grown under natural conditions. The parameters, Chlorophyll a + b content (Cab), carotenoid (Cca), dry matter content (Cdm), indicator of leaf water content (Cw) and leaf mesophyll structure (N) and the simulated fluorescence from the experiment were compared with the measured values to validate the model under natural conditions. The results show a good correlation (coefficient of determination R2 = 0.7–0.9) with the measured data at wavelengths of 650–880 nm. However, there is a large relative error (RE) that extends up to 150% at the peak of the fluorescence curve. To improve the accuracy of the simulation, an inversion code containing the emission efficiency parameters for photosystems I and II was added, which retrieves FQE I and II from the measured fluorescence spectra. The evaluation results for all wavelengths and two peaks demonstrated a significant reduction in the error at the peak of the curve by the Fluspect model with the FQE inversion code. This new method reduced the overestimation of fluorescence from 150% to 20% for the RE, and the R2 value was higher than 0.9 at the spectra peaks. Additionally, the original plant parameter information remained mostly unchanged upon the addition of the inversion code.
Highlights
Photosynthesis is the most important photochemical process for organisms on Earth, with the sun as its energy source
The spectral range of sunlight required for photosynthesis (400–700 nm) is called photosynthetically active radiation (PAR); the absorbed energy from PAR is not fully utilized by the photochemical process, as part of it is lost as heat radiation and fluorescence [1]
To obtain a better comparison of the model performance, the simulated fluorescence and measured data are compared in Figure 4, along with the results that include fluorescence quantum yield efficiency of photosystem (FQE) inversion
Summary
Photosynthesis is the most important photochemical process for organisms on Earth, with the sun as its energy source. The spectral range of sunlight required for photosynthesis (400–700 nm) is called photosynthetically active radiation (PAR); the absorbed energy from PAR is not fully utilized by the photochemical process, as part of it is lost as heat radiation (primarily) and fluorescence [1]. The terrestrial vegetation’s carbon budget and GPP require information on physiological parameters [2]. These parameters can be estimated by the use of fluorescence emissions [3,4,5], and several studies have successfully simulated fluorescence to evaluate the in vivo status of plant growth [6,7,8,9,10]
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