title: Carbon fixation in eucalypts in the field : Analysis of diurnal variations in photosynthetic capacity.
abstract: The rate of CO2assimilation at light saturation and an intercellular CO2concentration of 350 μl 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 CO2uptake. 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 CO2response of net photosynthesis, as obtained at low intercellular CO2concentrations, 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 CO2concentration is discussed.
authors.affiliation: Research School of Biological Sciences, Australian National University, GPO Box 475, 2601, Canberra City, ACT, Australia.|Division of Forest Research, CSIRO, GPO Box 4008, 2600, Canberra City, ACT, Australia.
authors.forename: M
authors.initials: M
authors.lastname: Küppers
authors.affiliation: Division of Forest Research, CSIRO, GPO Box 4008, 2600, Canberra City, ACT, Australia.
authors.forename: A M
authors.initials: AM
authors.lastname: Wheeler
authors.affiliation: Research School of Biological Sciences, Australian National University, GPO Box 475, 2601, Canberra City, ACT, Australia.|Lehrstuhl für Pflanzenökologie, Universität Bayreuth, Postfach 3008, D-8580, Bayreuth, Federal Republic of Germany.
authors.forename: B I L
authors.initials: BI
authors.lastname: Küppers
authors.affiliation: Research School of Biological Sciences, Australian National University, GPO Box 475, 2601, Canberra City, ACT, Australia.
authors.forename: M U F
authors.initials: MU
authors.lastname: Kirschbaum
authors.affiliation: Research School of Biological Sciences, Australian National University, GPO Box 475, 2601, Canberra City, ACT, Australia.
authors.forename: G D
authors.initials: GD
authors.lastname: Farquhar
keywords: Acacia; Carboxylation efficiency; Eucalyptus; Photosynthetic capacity; Stomata