Can improved canopy light transmission ameliorate loss of photosynthetic efficiency in the shade? An investigation of natural variation in Sorghum bicolor

Authors: JAIKUMAR, NIKHIL - Illinois State University; STUTZ, SAMANTHA - University Of Illinois; FERNANDES, SAMUEL - University Of Illinois; LEAKEY, ANDREW D B - University Of Illinois; Bernacchi, Carl; BROWN, PATRICK - University Of California, Davis; LONG, STEPHEN - University Of Illinois

Submitted to: Journal of Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/28/2021
Publication Date: 6/1/2021
Citation: Jaikumar, N.S., Stutz, S.S., Fernandes, S.B., Leakey, A.D.B., Bernacchi, C.J., Brown, P.J., Long, S.P. 2021. Can improved canopy light transmission ameliorate loss of photosynthetic efficiency in the shade? An investigation of natural variation in Sorghum bicolor. Journal of Experimental Botany. 72(13):4965-4980. https://doi.org/10.1093/jxb/erab176.
DOI: https://doi.org/10.1093/jxb/erab176

Interpretive Summary: Plants use the energy in sunlight to grow, a process called photosynthesis. The efficiency in which some plants, such as corn, use this light gets worse as you measure it from the top to the bottom of the plant. This loss of efficiency has a negative impact on crop growth because less efficient light use at the bottom of the plant means lower photosynthesis and lower growth. This experiment tested to see whether plants that have more erect leaves, which allows more light to the bottom of the plant, has higher efficiency than plants with leaves that droop, allowing less light to the bottom of the plant. The results from this research showed that the efficiency of light use dropped from the top to bottom of the plants, but the drop was worse when plants had drooping leaves and not as bad when the leaves were erect. This shows that how the leaves are oriented in a plant canopy can have a major impact on the growth, and ultimately yield potential, of the plant.

Technical Abstract: Previous studies have found that maximum quantum yield of CO2 assimilation (FCO2,max,app) declines in lower canopies of maize and Miscanthus, a maladaptive response to self-shading. These observations were limited to single genotypes, leaving it unclear that the maladaptive shade response is a general property of this C4 grass tribe, the Andropogoneae. We explored the generality of this maladaptation by testing the hypothesis that erect leaf forms (erectophiles), which allow more light into the lower canopy, suffer less of a decline in photosynthetic efficiency than drooping leaf (planophile) forms. On average, FCO2,max,app declined 27% in lower canopy leaves across 35 accessions, but the decline was over twice as great in planophiles than in erectophiles. The loss of photosynthetic efficiency involved a decoupling between electron transport and assimilation. This was not associated with increased bundle sheath leakage, based on 13C measurements. In both planophiles and erectophiles, shaded leaves had greater leaf absorptivity and lower activities of key C4 enzymes than sun leaves. The erectophile form is considered more productive because it allows a more effective distribution of light through the canopy to support photosynthesis. We show that in sorghum, it provides a second benefit, maintenance of higher FCO2,max,app to support efficient use of that light resource.