Photosynthesis Research

, Volume 105, Issue 1, pp 15–25 | Cite as

Altered physiological function, not structure, drives increased radiation-use efficiency of soybean grown at elevated CO2

  • Uwe Rascher
  • Bernhard Biskup
  • Andrew D. B. Leakey
  • Justin M. McGrath
  • Elizabeth A. Ainsworth
Regular Paper


Previous studies of elevated carbon dioxide concentration ([CO2]) on crop canopies have found that radiation-use efficiency is increased more than radiation-interception efficiency. It is assumed that increased radiation-use efficiency is due to changes in leaf-level physiology; however, canopy structure can affect radiation-use efficiency if leaves are displayed in a manner that optimizes their physiological capacity, even though the canopy intercepts the same amount of light. In order to determine the contributions of physiology and canopy structure to radiation-use and radiation-interception efficiency, this study relates leaf-level physiology and leaf display to photosynthetic rate of the outer canopy. We used a new imaging approach that delivers three-dimensional maps of the outer canopy during the growing season. The 3D data were used to model leaf orientation and mean photosynthetic electron transport of the outer canopy to show that leaf orientation changes did not contribute to increased radiation-use; i.e. leaves of the outer canopy showed similar diurnal leaf movements and leaf orientation in both treatments. Elevated [CO2] resulted in an increased maximum electron transport rate (ETRmax) of light reactions of photosynthesis. Modeling of canopy light interception showed that stimulated leaf-level electron transport at elevated [CO2], and not alterations in leaf orientation, was associated with stimulated radiation-use efficiency and biomass production in elevated [CO2]. This study provides proof of concept of methodology to quantify structure–function relationships in combination, allowing a quantitative estimate of the contribution of both effects to canopy energy conversion under elevated [CO2].


Three-dimensional canopy surface Photosynthesis Light reactions Chlorophyll fluorescence Elevated CO2 Glycine max Structure–function relations 



Leaf incidence angle, i.e. angle between sun and leaf normal


Leaf absorbance, i.e. proportion of absorbed PPFD


Photosynthetic CO2 uptake rate (μmol m−2 s−1)


Photosynthetic electron transport rate (μmol electrons m−2 s−1)


Maximum photosynthetic electron transport rate at light saturation (μmol electrons m−2 s−1)


Fluorescence of the light-adapted leaf


Minimum fluorescence of the dark-adapted leaf


Maximum fluorescence of the dark-adapted leaf

\( F^{\prime}_{\text{m}} \)

Maximum fluorescence of the light-adapted leaf


Maximum quantum efficiency of PS II (F v = F m − F 0)


Leaf area index (m2 of leaf/m2 of ground)


Photosynthetic photon flux density (λ = 400–700 nm) (μmol photons m−2 s−1)


Direct photosynthetic photon flux density on a horizontal surface (λ = 400–700 nm) (μmol photons m−2 s−1)


Diffuse photosynthetic photon flux density (λ = 400–700 nm) (μmol photons m−2 s−1)


Effective incident photosynthetic photon flux density on the leaf surface (λ = 400–700 nm) (μmol photons m−2 s−1)




Maximum apparent carboxylation capacity of Rubisco (μmol m−2 s−1)

\( \Updelta F /F^{\prime}_{\text{m}} \)

Effective quantum efficiency of PS II (\( \Updelta F = F^{\prime}_{\text{m}} - F \)) measured at ambient light



We thank Tim Mies for technical assistance, and Steve Long for supporting our research at SoyFACE. SoyFACE was supported by the Illinois Council for Food and Agricultural Research, Archer Daniels Midland Company, the U.S. Department of Agricultural, and the Illinois Agricultural Experiment Station. B. Biskup and U. Rascher were supported by a NSF/DAAD grant (grant PPP D/05/50496). B. Biskup also acknowledges support of his PhD thesis by the Heinrich-Heine University of Düsseldorf, Germany. We thank K.G. Rascher for assistance with the statistical analyses, and D. Ort for valuable discussions. We also greatly thank H. Scharr for supporting the development of the stereo system and the development of the analyses algorithms.


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Copyright information

© Springer Science+Business Media B.V. 2010

Authors and Affiliations

  • Uwe Rascher
    • 1
  • Bernhard Biskup
    • 1
  • Andrew D. B. Leakey
    • 2
    • 3
  • Justin M. McGrath
    • 2
  • Elizabeth A. Ainsworth
    • 2
    • 3
    • 4
  1. 1.Institute of Chemistry and Dynamics of the Geosphere: ICG-3Forschungszentrum Jülich GmbHJülichGermany
  2. 2.Department of Plant BiologyUniversity of Illinois, Urbana-ChampaignUrbanaUSA
  3. 3.Institute for Genomic BiologyUniversity of Illinois, Urbana-ChampaignUrbanaUSA
  4. 4.U.S. Department of Agriculture, Photosynthesis Research Unit, Agricultural Research ServiceUrbanaUSA

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