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Leaf gas exchange and carbon isotope composition responses to drought in a drought-avoiding (Pinus pinaster) and a drought-tolerant (Quercus petraea) species under present and elevated atmospheric CO2 concentrations

Authors

  • C. PICON,

    1. Unité d'Ecophysiologie Forestière, Equipe Bioclimatologie- Ecophysiologie, INRA Nancy, F-54280 Champenoux, France
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  • J. M. GUEHL,

    Corresponding author
    1. Unité d'Ecophysiologie Forestière, Equipe Bioclimatologie- Ecophysiologie, INRA Nancy, F-54280 Champenoux, France
      Jean-Marc Guehl, Unité de recherches en Ecophysiologie Forestière, Equipe de Bioclimatologie et Ecophysiologie, INRA Nancy, F-54280 Champenoux, france.
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  • A. FERHI

    1. Centre de Recherches Géodynamiques, Université Paris VI, 47, Avenue de Corzent, F-74203 Thonon-les-Bains, France
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Jean-Marc Guehl, Unité de recherches en Ecophysiologie Forestière, Equipe de Bioclimatologie et Ecophysiologie, INRA Nancy, F-54280 Champenoux, france.

ABSTRACT

The responses of predawn leaf water potential (φwp), leaf conductance to water vapour diffusion (g), CO2 assimilation rate (A) and carbon isotope competition (δ13C) to a soil drying cycle were assessed in Pinus pinaster, a drought-avoiding species with high stomatal sensitivity to drought, and Quercus petraea, a drought-tolerant species with lower stomatal sensitivity to drought, under present (350 μmol−1) and elevated (700 μmol−1) atmospheric CO2 concentrations ([CO2]). In P. pinaster, decreasing A in response to drought was associated with increasing plant intrinsic water use efficiency (A/g) and with decreasing calculated intercellular [CO2] (C1), suggesting a stomatal limitation of A. In contrast, in Q. petraea, A/g declined and C1 increased during the drying cycle, which suggests a non-stomatal origin for the decrease in A. In P. pinaster, a negative relationship was observed between the gas exchange-derived values of Ci/Ca and δ13C, which conforms to the classical two-step carbon isotope discrimination model. In Q. petraea, the relationship between C1/Ca and δ13C was positive. Possible causes of this discrepancy are discussed. Lower g values were observed under elevated [CO2] than under present [CO2] in Q. petraea, whereas g was unaffected in P. pinaster. A stimulation of A by elevated [CO2] was found in P. pinaster but not in Q. petraea. In both species, A/g was markedly higher under elevated than under present [CO2]. Whether the differences in the g response to elevated [CO2] found here can be generalized to other drought-avoiding and non-avoiding species remains to be assessed.

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