The inverse relationship between solar-induced fluorescence yield and photosynthetic capacity: benefits for field phenotyping

Authors: PENG, FU - University Of Illinois; MEACHAM-HENSOLD, KATHERINE - University Of Illinois; Siebers, Matthew; Bernacchi, Carl

Submitted to: Journal of Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/2/2020
Publication Date: 2/24/2021
Citation: Peng, F., Meacham-Hensold, K., Siebers, M.H., Bernacchi, C.J. 2021. The inverse relationship between solar-induced fluorescence yield and photosynthetic capacity: benefits for field phenotyping. Journal of Experimental Botany. 72(4):1295-1306. https://doi.org/10.1093/jxb/eraa537.
DOI: https://doi.org/10.1093/jxb/eraa537

Interpretive Summary: Plants absorb sunlight. The primary purpose of absorbing this sunlight is to grow using the process called photosynthesis. A small amount of this absorbed light is released from the plant and this is called chlorophyll fluorescence. Scientists refer to this light being released as solar-induced fluorescence which is abbreviated as SIF. Measuring SIF is linked to photosynthesis because SIF and photosynthesis "compete" with each other. Most SIF measurements are made on whole fields or on entire regions of the planet using satellites. The research in this manuscript looks to use lower-cost and very fast techniques to see if SIF can be measured at small scales. The results of this work shows that advanced cameras can be used to measure SIF on plots which are pretty small and which are typically used to breed crops to be more productive. This research also shows strong relationships between SIF and what is measured using traditionally slow and expensive techniques. This research can be used to advance understanding of how breeding productive crops is linked with higher photosynthetic rates.

Technical Abstract: Improving photosynthesis is considered a promising way to increase crop yield to feed a growing population. Realizing this goal requires non-destructive techniques to quantify photosynthetic variation among crop cultivars. Despite existing remote sensing-based approaches to mapping photosynthetic capacity, it remains a question whether solar-induced fluorescence (SIF) can facilitate screening crop cultivars of improved photosynthetic capacity in plant breeding trials. Here we tested a relevant hypothesis relating SIF and SIF yield with the electron transport rate (i.e., Jmax). Time-synchronized hyperspectral images and irradiance spectra of sunlight under clear-sky conditions were combined to estimate SIF and SIF yield, which were then correlated with ground-truth photosynthetic variables (Vcmax and Jmax) obtained from portable leaf gas exchange systems. With observations binned over time (i.e., group 1: July 6 - 12, 2017, group 2: July 18 - 31, 2017, and group 3: July 24 - 25, 2018), SIF yield showed a stronger negative relationship, compared to SIF, with photosynthetic variables. Specifically, using SIF yield for Jmax (Vcmax) predictions, the regression analysis exhibited an R2 of 0.62 (0.71) and RMSE of 11.88 (46.86) µmol m-2 s-1 for group 1, an R2 of 0.85 (0.72) and RMSE of 13.51 (49.32) µmol m-2 s-1 for group 2, and an R2 of 0.92 (0.87) and RMSE of 15.23 (30.29) µmol m-2 s-1 for group 3. The good proxy of SIF yield for Vcmax was explained by the strong correlation between Jmax and Vcmax. The observed negative relationship between SIF yield and photosynthetic variables was mainly attributed to the positive relationship between APAR and photosynthetic variables. Overall, the combined use of hyperspectral images and irradiance measurements allows better and faster characterization of photosynthetic parameters at plot level compared to reflectance spectra alone. This linearly inversed relationship has the potential to further accelerate development of crop cultivars of improved photosynthesis.