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

Abstract

Chlorophyll fluorescence can be remotely sensed in open fields via the Fraunhofer atmospheric absorption lines of oxygen and is termed Solar-Induced Fluorescence (SIF). SIF has been extensively related to carbon assimilation at global ecology scale and was interpreted as electron transport rate. However, SIF was shown to be unrelated directly to carbon assimilation at finer-scale resolution and may be related to other photosynthetic processes, such as non-photochemical quenching. This raises the question how exactly the SIF relates to actual photosynthetic activity. Based on a recently introduced spectral index that relates the photochemical fraction of SIF to the actual electron transport rate, this study presents the formulation of a structural equation, relating the remotely sensed electron transport rate index to fluorescence yield which considers the various fates of energetic quanta and electron excitation. The proposed structural equations are used to examine and interpret the relation between the novel spectral index and seasonal growth of corn (Z. mays Sh2, ‘super sweet’) on a platform of fertilization concentration gradient. Potential uses, practical and theoretical, for the proposed structural equations are discussed.

Limitations of Solar-Induced Chlorophyll Fluorescence (SIF) for Estimating Photosynthesis Under Stress

“…There was significant positive (logarithmic) correlation between RS-ETRi and the plant weight measured by the FPP ( Figure 3F ). This is expected in view of the logarithmic correlation between the special SIF term within this index (Liran, 2022) which implies for complex relationship between light use efficiency and biomass production.…”

“…Liran et al (2020) suggested a new spectral index which is based on SIF and correlates with electron transport rate of the light reactions of plants in order to bypass the high spatial resolution dissociation problem. Further, Liran (2022) shows that this index -Remote Sensing of Electron Transport Rate (RS-ETR) interprets the fluorescence emission as Light Use Efficiency of the photosynthetic apparatus of the crop that it measures, thus relating photochemistry to SIF properties. only few works have tried to link SIF with water status-related traits (Lu et al, 2018;Xu et al, 2018).…”

Solar Induced Fluorescence Retrieved from Avocado (Persea americanaMill.) Canopies Along the Season Correlates with Sugar Levels in the Developing Fruit

“…Spectral acquisition was performed as described in Liran (LIRAN 2022). Two STS-VIS micro-spectroradiometers (STS-VIS Developer kit, OceanInsight, Largo, FL, USA) acquired the spectra simultaneously -one was mounted on the drone which retrieved upwelling radiance from the crops (AIR unit) and the second was mounted on a stand at the ground retrieving upwelling radiance from a reference plate (94% reflectance plate, Permaflect ® , LabSphere, USA) (GROUND unit).…”