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

Institute of Chemistry and Dynamics of the Geosphere ICG-3, Forschungszentrum Jülich GmbH, Leo-Brandt-Strasse, 52425 Jülich, Germany.
Photosynthesis Research (Impact Factor: 3.5). 07/2010; 105(1):15-25. DOI: 10.1007/s11120-010-9548-6
Source: PubMed


Previous studies of elevated carbon dioxide concentration ([CO(2)]) 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 [CO(2)] resulted in an increased maximum electron transport rate (ETR(max)) of light reactions of photosynthesis. Modeling of canopy light interception showed that stimulated leaf-level electron transport at elevated [CO(2)], and not alterations in leaf orientation, was associated with stimulated radiation-use efficiency and biomass production in elevated [CO(2)]. 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 [CO(2)].

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    • "In a first case study, we were able to use this stereo system to quantify diurnal changes in leaf orientations in soybean. Highly resolved data on leaf angle distribution, together with forward modelling of sun movement and light penetration in a complex 3- D canopy, leads to a better understanding of the interplay of structural and functional properties in radiation use in natural canopies (Rascher et al. 2010a). "
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    • "The maximum electron transport rate (ETRmax) of light reactions of photosynthesis, one of the chlorophyll fluorescence parameters to evaluate the changes of leaf photosynthesis, was reported to increase under elevated [CO2] [19]. Elevated [CO2] could also change the leaf ultrastructure and increase the amount of starch in chloroplasts [20]–[23], which may affect photosynthetic capacity. "
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    • "The photochemical efficiency of photosystem II (FqЈ/FmЈ) was determined by measuring steadystate fluorescence and maximum fluorescence during a light-saturating pulse of ~6500 mmol m -2 s -1 following the procedures of Genty, Briantais & Baker (1989). The efficiency of CO2 assimilation (FCO2) was determined according to Naidu & Long (2004) using average leaf absorbance measurements determined at SoyFACE by Rascher et al. (2010). In 2008, gas exchange was measured during vegetative growth on 31 July 2008 (vegetative stage 7; Fehr et al. 1971). "
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