A Mathematical Model of Photosynthetic Electron Transport in Response to the Light Spectrum Based on Excitation Energy Distributed to Photosystems

Abstract

To enable us to analyze more systematically the effects of the spectral distribution of light (i.e. light quality) on photosynthetic electron transport, we propose a simple mathematical model which describes electron transport reactions under light-limited conditions based on the excitation energy distributed to the photosystems. The model assumes that the rate-limiting photosystem performs the photochemical reaction at its maximum yield, while the yield in the other photosystem is passively down-regulated to equalize the rates of linear electron transport through the photosystems. Using intact cucumber leaves, we tested the model by comparing actual and estimated photosynthetic parameters under several combinations of photon flux densities of red and far-red lights (R and FR, respectively). Simultaneously provided R and FR yielded greater gross photosynthetic rates than the sums of the rates under only R and only FR, which is known as the 'enhancement effect'. The present model reproduced these non-additive increases in the gross photosynthetic rates in response to supplemental FR to R and provided more accurate estimates than an existing method that did not take the enhancement effect into account (root mean square errors: 0.11 and 0.21 μmol m-2 s-1, respectively). Using the present model, the photon flux density of the supplemental FR which gives the changing point of rate-limiting photosystem and the photochemical yields of the non-rate-limiting photosystems were estimated reasonably well. The present study has therefore formulated a simplified quantitative electron transport model in response to the light spectrum based on generally accepted concepts and demonstrated its validity experimentally.

Far‐red photons have equivalent efficiency to traditional photosynthetic photons: Implications for redefining photosynthetically active radiation

“…This view is based on the low action/quantum yield of photosynthesis under monochromatic far‐red light (Emerson & Lewis, ; Inada, ; McCree, ). Recent studies have revisited the Emerson enhancement effect and demonstrated the significance of the synergistic interaction between far‐red and shorter wavelengths on leaf photosynthesis (Hogewoning et al, ; Kono et al, 2020; Murakami et al, ; Zhen & van Iersel, ). It remained unclear, however, if the photosynthetic efficiency of far‐red photons at single leaf or canopy level is comparable with traditionally defined photosynthetic photons.…”

“…Recently, a growing body of research indicates that under broad spectrum or combined lights, plants can use far‐red photons more efficiently for photosynthesis than previously thought (Hogewoning et al, ; Murakami, Matsuda, & Fujiwara, ; Zhen & van Iersel, ). Hogewoning et al () observed that the quantum yield for CO 2 fixation in cucumber measured under broad spectral light (wavelength range of 400–725 nm) is 10% to 21% higher, depending on the growth light spectra and intensity, than the weighted sum of the quantum yield determined at 19 wavelengths across the same spectral range.…”

Green Light Improves Photosystem Stoichiometry in Cucumber Seedlings (Cucumis sativus) Compared to Monochromatic Red Light

“…It is possible that the red and green light enhancement can be described in part by the ‘enhancement effect’ or ‘Emerson effect’ which refers to the phenomenon where photosynthesis from combined spectra can be greater than the sum of its parts due to excitation energy distribution between photosystem I and photosystem II [ 34 , 35 , 36 ].…”

Substituting Far-Red for Traditionally Defined Photosynthetic Photons Results in Equal Canopy Quantum Yield for CO2 Fixation and Increased Photon Capture During Long-Term Studies: Implications for Re-Defining PAR

“…More recent work demonstrates that most of the shorter wavelength photons from 400 to 680 nm over-excite photosystem II (PSII), while longer wavelength far-red photons preferentially excite photosystem I (PSI) (Evans, 1987;Hogewoning et al, 2012;Laisk et al, 2014;Zhen et al, 2018). When combining far-red with shorter wavelength photons, the balance of excitation distribution between PSII and PSI is restored, thus leading to increased leaf photochemical efficiency (Zhen and van Iersel, 2017) and photosynthetic rate (Hogewoning et al, 2012;Murakami et al, 2018). Scaling up from leaf to canopy level, Zhen and Bugbee (2020) found that far-red photons (700-750 nm) are equally efficient at driving canopy photosynthesis when added to 400 to 700 nm photons in 14 diverse crop species.…”