Carbon fixation in eucalypts in the field |
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Authors: | M. Küppers A. M. Wheeler B. I. L. Küppers M. U. F. Kirschbaum G. D. Farquhar |
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Affiliation: | (1) Research School of Biological Sciences, Australian National University, GPO Box 475, 2601 Canberra City, ACT, Australia;(2) Division of Forest Research, CSIRO, GPO Box 4008, 2600 Canberra City, ACT, Australia;(3) Lehrstuhl für Pflanzenökologie, Universität Bayreuth, Postfach 3008, D-8580 Bayreuth, Federal Republic of Germany;(4) Present address: Lehrstuhl für Pflanzenökologie, Universität Bayreuth, Postfach 3008, D-8580 Bayreuth, FR Germany |
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Abstract: | Summary The rate of CO2 assimilation at light saturation and an intercellular CO2 concentration of 350 l l-1 (photosynthetic capacity), measured in leaves of Eucalyptus pauciflora, E. behriana, E. delegatensis and Acacia melanoxylon, declined over the course of cloudless days under naturally varying environmental conditions as well as under constant optimal conditions for high CO2 uptake. Since the capacity did not recover during the light period, it was different from the midday depression of gas exchange. The change appeared to be caused neither by the diurnal variation of total leaf water potential, by photoinhibition of redox-reaction centres in photosystems nor by changes in the intrinsic properties of Ribulose-bisphosphate carboxylase-oxygenase. The decline was more pronounced in winter than in summer. It was related to the duration of illumination or the cumulative carbon gain. It was reversible in the following dark phase, and it did not occur on changeable days with short peaks of high light.Despite the decline in photosynthetic capacity, the initial slope of the CO2 response of net photosynthesis, as obtained at low intercellular CO2 concentrations, remained constant during the day, but declined at night when photosynthetic capacity recovered. In all cases stomatal conductance varied in parallel with photosynthetic capacity. The relevance of changes in photosynthetic capacity for the intercellular CO2 concentration is discussed.Abbreviations and symbols A CO2 assimilation - ABA abscisic acid - Ac350 photosynthetic capacity at ci=350l l-1 - ci intercellular CO2 concentration - g leaf conductance to water vapour - I photon flux density (irradiance) - P air pressure - Pi inorganic phosphate - Rd net CO2 release at * - Rubisco Ribulose-bisphosphate carboxylase-oxygenase - RuBP Ribulose-bisphosphate - T leaf temperature - w leaf-to-air water vapour concentration difference - A/ci carboxylation efficiency at low ci - * light-independent CO2 compensation point - total leaf water potential |
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Keywords: | Photosynthetic capacity Stomata Carboxylation efficiency Eucalyptus Acacia |
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