Long-term growth of soybean at elevated [CO2] does not cause acclimation of stomatal conductance under fully open-air conditions

Authors

  • ANDREW D. B. LEAKEY,

    Corresponding author
    1. Institute for Genomic Biology and Department of Plant Biology, University of Illinois at Urbana-Champaign, 1207 West Gregory Drive, Urbana, IL 61801, USA,
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  • CARL J. BERNACCHI,

    1. Center for Atmospheric Science, Illinois State Water Survey, 2204 Griffith Dr, Champaign, IL 61820, USA,
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  • DONALD R. ORT,

    1. Institute for Genomic Biology and Department of Plant Biology, University of Illinois at Urbana-Champaign, 1207 West Gregory Drive, Urbana, IL 61801, USA,
    2. Photosynthesis Research Unit, US Department of Agriculture/Agricultural Research Service, 1201 West Gregory Drive, Urbana, IL 61801, USA and
    3. Department of Crop Sciences, University of Illinois at Urbana-Champaign, 1201 West Gregory Drive, Urbana, IL 61801, USA
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  • STEPHEN P. LONG

    1. Institute for Genomic Biology and Department of Plant Biology, University of Illinois at Urbana-Champaign, 1207 West Gregory Drive, Urbana, IL 61801, USA,
    2. Department of Crop Sciences, University of Illinois at Urbana-Champaign, 1201 West Gregory Drive, Urbana, IL 61801, USA
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Andrew D. B. Leakey. Fax: +1 217 265 6800; e-mail: leakey@life.uiuc.edu

ABSTRACT

Accurately predicting plant function and global biogeochemical cycles later in this century will be complicated if stomatal conductance (gs) acclimates to growth at elevated [CO2], in the sense of a long-term alteration of the response of gs to [CO2], humidity (h) and/or photosynthetic rate (A). If so, photosynthetic and stomatal models will require parameterization at each growth [CO2] of interest. Photosynthetic acclimation to long-term growth at elevated [CO2] occurs frequently. Acclimation of gs has rarely been examined, even though stomatal density commonly changes with growth [CO2]. Soybean was grown under field conditions at ambient [CO2] (378 µmol mol−1) and elevated [CO2] (552 µmol mol−1) using free-air [CO2] enrichment (FACE). This study tested for stomatal acclimation by parameterizing and validating the widely used Ball et al. model (1987, Progress in Photosynthesis Research, vol IV, 221–224) with measurements of leaf gas exchange. The dependence of gs on A, h and [CO2] at the leaf surface was unaltered by long-term growth at elevated [CO2]. This suggests that the commonly observed decrease in gs under elevated [CO2] is due entirely to the direct instantaneous effect of [CO2] on gs and that there is no longer-term acclimation of gs independent of photosynthetic acclimation. The model accurately predicted gs for soybean growing under ambient and elevated [CO2] in the field. Model parameters under ambient and elevated [CO2] were indistinguishable, demonstrating that stomatal function under ambient and elevated [CO2] could be modelled without the need for parameterization at each growth [CO2].

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