Addition of longer wavelength absorbing chlorophylls into crops could increase their photosynthetic productivity by 26

Abstract

Crop leaves absorb approximately 90% of visible photons (400 - 700 nm) but transmit or reflect most far-red (FR) photons (700 - 800 nm). However, some cyanobacteria use FR photons up to 800 nm by incorporating chlorophyll (Chl) d or/and f into their photosystems. Here, we use a 3D canopy model to evaluate whether introducing these pigments could improve photosynthetic performance of field grown soybean. We simulate photon absorption and CO₂ assimilation show that the introduction of Chl d and f would significantly enhance photosynthesis, especially in the lower canopy, where visible light is depleted and FR light is abundant. When FR absorption is regulated by phytochrome-sensed FR/red (FR/R) photon ratio, the benefit is further increased, with canopy CO₂ assimilation improving up to 26%, without increasing the risk of photodamage. These results show that introducing FR-absorbing Chls into crops could have great value in boosting productivity.

Fig. 1. Light spectrum and absorbed light distribution in a soybean canopy.

a Photon flux density (PFD) of a solar spectrum at top of the canopy, as defined by the standards of an inclined plane at a 37° tilt toward the equator facing the sun (https://www.nrel.gov/grid/solar-resource/spectra-am1.5.html). The PFD at each wavelength was calculated from the solar spectrum’s energy and the energy per photon at that wavelength (Eq. (1)). Shaded areas correspond to the 400–700 nm range (continuous spectrum), 700–750 nm (red) and 750–800 nm (burgundy). b The sum of incident visible (V) photon flux distribution in a soybean canopy (leaf area index of 6.9), including blue (400–500 nm), green (501–600 nm) and red (601–700 nm) photon; c The leaf net CO₂ assimilation rate utilizing visible photon (A_V) in the canopy. d Incident far-red photon (701–800 nm) in the soybean canopy with leaf FR absorption fraction of 0.1 (Abs_FR=0.1). Source data are provided as a Source Data file.

Fig. 2. The impact of Chl d (701–750 nm far-red light) utilization on canopy net CO₂ assimilation rate (Ac), the absorbed light, transpiration rate (Ec) and water use efficiency (WUE) at different stages of soybean growth in Champaign, IL, USA.

a The soybean canopy of different date of year (DOY). Leaf area index (LAI) was 0.05, 0.49, 2.1 6.1 and 6.9 for the 5 simulated dates, respectively. b, c Present the Ac and the absorbed light of the soybean canopy at different times of the day. d Shows the effect of different Abs_FR settings on daily average light absorption, Ac, Ec and WUE. V visible photons, FR far-red photons. Abs_FR, leaf FR absorption fraction. Source data are provided as a Source Data file.

Fig. 3. The impact of Chl d (701–750 nm FR) utilization on canopy net CO₂ assimilation rate (Ac).

Two different strategies for setting leaf absorption fraction of FR (Abs_FR) were tested: Strategy 1 (a, c, e) with constant Abs_FR, and Strategy 2 (b, d, f) with Abs_FR varies linearly with the${Ratio}_{FR/R}$ (${Abs}_{FR}=k\cdot {Ratio}_{FR/R}$) in the soybean canopy(Aug 18th, 2023, in Champaign, IL, USA). a, b Display the Abs_FR values at various canopy heights. Simulated daily average incident far-red (730 ± 5 nm) to red (667 ± 5 nm) photon flux ratio (FR/R ratio) for each leaf pixel (blue dots) using ray tracing algorithm, with the average incident FR/R ratio of each canopy layer (every 10 cm in height, Supplementary Table 5) marked by black dots. Leaf FR absorption fraction was set as 0.3. k is set to 0.056, which was obtained by scaling the Abs_FR at bottom of the canopy to the value of 0.86, which is the maximum absorption fraction from the measurement (Supplementary Fig. 1, Supplementary Tables 1, 6). c, d Simulated far-red photons (FR, 701–750 nm) absorption of a soybean canopy with the two strategies respectively. e, f The enhancement of leaf net CO₂ assimilation with additional far-red photon (A_V+FR-A_V). g Depicts the Ac and h presents the absorbed light of the soybean canopy at different times of the day for both strategies. Source data are provided as a Source Data file.

Fig. 4. Impact of Chl f utilization on canopy CO₂ assimilation and light absorption.

Simulated canopy net CO₂ assimilation rate (Ac) and absorbed light throughout the day (Aug 18th, 2023, Champaign, IL, US) in a soybean canopy with constant Abs_FR of 0.1, and with Abs_FR varies with the ${Ratio}_{FR/R}$$\left({Abs}_{FR}=k\cdot {Ratio}_{FR/R}\right)$, where k is set to 0.056. a, b Show Ac and absorbed light changes with the two strategies. Leave with Chl f used FR photons (701–760 or 800 nm). c, d The enhancement of leaf net CO₂ assimilation from additional FR photons (A_V+FR- A_V) at noon, where FR represents in FR photons of 701–800 nm. Source data are provided as a Source Data file.