A branch bag technique for simultaneous CO2 enrichment and assimilation measurements on beech (Fagus sylvatica L.)

Authors

  • E. DUFRENE,

    1. Laboratoire d'Ecologie Végétale, CNRS URA 1492 Bat. 362, Université Paris Sud-Orsay, 91405 Orsay Cedex, France
    Search for more papers by this author
  • J.-Y. PONTAILLER,

    Corresponding author
    1. Laboratoire d'Ecologie Végétale, CNRS URA 1492 Bat. 362, Université Paris Sud-Orsay, 91405 Orsay Cedex, France
      Jean-Yves Pontailler, Laboratoire d'Ecologie Végétale, CNRS URA 1492 Bât. 362, Université Paris Sud-Orsay, 91405 Orsay Cedex, France.
    Search for more papers by this author
  • B. SAUGIER

    1. Laboratoire d'Ecologie Végétale, CNRS URA 1492 Bat. 362, Université Paris Sud-Orsay, 91405 Orsay Cedex, France
    Search for more papers by this author

  • This study was supported by the 'EPOCH COTU 13′ collaborative EC project, coordinated by P.G. Jarvis (University of Edinburgh). The authors acknowledge Marianne Mousseau for stimulating discussions, Jean Guittet, Bernard Legay and Jacqueline Liebert for their help in the field and in the laboratory. 1CI France kindly provided free polyethylene film and Eurosep, the Li-Cor representative in France, lent us new radiation sensors.

Jean-Yves Pontailler, Laboratoire d'Ecologie Végétale, CNRS URA 1492 Bât. 362, Université Paris Sud-Orsay, 91405 Orsay Cedex, France.

ABSTRACT

A cheap CO2 enrichment system was designed to perform continuous gas exchange measurements of branches of mature European beech trees (Fagus sylvatica L.). Branches were grown at ambient (350 cm3 m-3) and elevated CO2 (700cm3 m-3) during the whole 1992 leafy period. Leaks resulting from airtightness defaults in the system appeared to be low enough to measure accurately net CO2 assimilation and transpiration rates during the day. However, the CO2 exchange rates during the night (respiration) were too low to allow accurate measurements. Elevated CO2 had a great effect on the net assimilation rate of branches via its influence on both the C3 photosynthetic pathway and the shade-tolerance of beech trees (85% increase). The A/Ca curves showed no acclimation effect to high CO2, both control and enriched branches increasing their net assimilation in the same way. The decrease of net assimilation rates in mature leaves was similar for both control and enriched branches. The pattern of daily transpiration rates remained the same for both control and enriched branches, hence we can assume that there was no visible CO2 effect on stomata.

Ancillary