title: Analysis of gas exchange in seedlings of Acer saccharum: integration of field and laboratory studies.
abstract: In the field, photosynthesis of Acer saccharum seedlings was rarely light saturated, even though light saturation occurs at about 100 μmol quanta m-2s-1photosynthetic photon flux density (PPFD). PPFD during more than 75% of the daylight period was 50 μmol m-2s-1or less. At these low PPFD's there is a marked interaction of PPFD with the initial slope (CE) of the CO2response. At PPFD-saturation CE was 0.018 μmol m-2s-1/(μl/l). The apparent quantum efficiency (incident PPFD) at saturating CO2was 0.05-0.08 mol/mol. [Formula: see text] and PPFD-saturated CO2exchange was 6-8 μmol m-2s-1. The ratio of internal CO2concentration to external (Ci/Ca) was 0.7 to 0.8 except during sunflecks when it decreased to 0.5. The decrease in Ci/Caduring sunflecks was the result of the slow response of stomates to increased PPFD compared to the response of net photosynthesis. An empirical model, which included the above parameters was used to simulate the measured CO2exchange rate for portions of two days. Parameter values for the model were determined in experiments separate from the daily time courses being sumulated. Analysis of the field data, partly through the use of simulations, indicate that the elimination of sunflecks would reduce net carbon gain by 5-10%.
authors.affiliation: Biological Station and Botanical Gardens, University of Michigan, 48109-1048, Ann Arbor, MI, USA.
authors.forename: J A
authors.initials: JA
authors.lastname: Weber
authors.affiliation: Biological Station and Botanical Gardens, University of Michigan, 48109-1048, Ann Arbor, MI, USA.
authors.forename: T W
authors.initials: TW
authors.lastname: Jurik
authors.affiliation: Biological Station and Botanical Gardens, University of Michigan, 48109-1048, Ann Arbor, MI, USA.
authors.forename: J D
authors.initials: JD
authors.lastname: Tenhunen
authors.affiliation: Biological Station and Botanical Gardens, University of Michigan, 48109-1048, Ann Arbor, MI, USA.
authors.forename: D M
authors.initials: DM
authors.lastname: Gates