Novel Remote Sensing Index of Electron Transport Rate Predicts Primary Production and Crop Health in L. sativa and Z. mays

Abstract

Photosynthesis performance can be assessed quantitatively with light response curves. These curves record the Electron Transport Rate (ETR) as a function of light intensity. Then, statistical fit on these curves parameterize light use efficiency, maximum photosynthetic activity and the reaction of the apparatus to stress. While this technique is performed with portable fluorometers in field conditions, it is difficult to scale it to the canopy level. The Fraunhofer line discrimination technique, which detects fluorescence signals emitted during photosynthesis, is a promising method to assess photosynthetic performance of canopies. In this study, we define a remote sensing ETR index based on a combination of three parameters: sun-induced fluorescence, normalized differential vegetation index and light intensity. Two representatives of C3 and C4 photosynthesis, L. sativa and Z. mays, experienced a fertilization concentrations gradient. ETR increased with light intensity in both crops. In L. sativa, ETR assumed a linear relationship between the photosynthetic activity and light intensity, with a correlation of R2 = 0.99 to the portable fluorometer. Additional parametrization revealed a resilience of its reaction centers to photoinhibition in maximum light intensities. When Z. mays experienced open field conditions, ETR correlated with the plant’s status. While the results of this study are promising, the index still requires validation in terms of temporal track and spatial variability.

Formulation of a Structural Equation Relating Remotely Sensed Electron Transport Rate Index to Photosynthesis Activity

“…Panel A contains data already presented in the original publication: "Novel Remote Sensing Index of Electron Transport Rate Predicts Primary Production and Crop Health in L. sativa and Z. mays". Available online: https://www.mdpi.com/20 72-4292/12/11/1718/htm [7] (accessed on 1 January 2022).…”

“…This communication suggests a structural formulation between the photosynthesis light reaction rate coefficients and the new spectral index for remote sensing of electron transport rate in plants (RS-ETRi) [7]. The RS-ETRi has a non-linear relationship with traditional vegetation indices-MTVI2 [13] and SIPI [14].…”

“…The experimental setup was described in the original study, Liran et al [7]. Generally, two units acquired reflected spectra simultaneously.…”

“…A possible explanation for this discrepancy is the fact that SIF measures the overall fluorescence emitted from the apparatus, which includes both fluorescence coming from photochemistry and fluorescence that is emitted from photoprotective mechanisms [6]. Recently, Liran et al [7] introduced a new spectral index, where the photochemical fraction of SIF was related to actual electron transport rate in the plant, and therefore, indirectly reported on biomass production: RS-ETRi W m −2 = I W m −2 •A• SIF 687 SIF 687 + SIF 760 (1) where RS-ETRi stands for Remote Sensing of Electron Transport Rate index, I is the intensity of Photosynthetically Active Radiation [W m −2 the photosynthetic apparatus (approximated by the established vegetation index NDVI-Normalized Differential Vegetation Index [8]), and SIF # is the Solar-Induced Fluorescence measured at 687 nm and 760 nm. This index, when measured 2 m above the plants, was highly correlated (R 2 = 0.99) with the ETR measured directly on leaves from the same plant community with a handheld fluorometer [7].…”

Metamitron, a Photosynthetic Electron Transport Chain Inhibitor, Modulates the Photoprotective Mechanism of Apple Trees

“…Each group of control or treatments within this study included 3 samples from each of the three branches taken from different trees in the orchard. Statistical procedures were performed as described in Liran et al (2020) [48]. Groups were checked for normal distribution with Shapiro-Wilk's test and homogeneity of variances with Levene's test.…”