Oecologia

, Volume 65, Issue 3, pp 338–347

Analysis of gas exchange in seedlings of Acer saccharum: integration of field and laboratory studies

  • J. A. Weber
  • T. W. Jurik
  • J. D. Tenhunen
  • D. M. Gates
Original Papers

DOI: 10.1007/BF00378907

Cite this article as:
Weber, J.A., Jurik, T.W., Tenhunen, J.D. et al. Oecologia (1985) 65: 338. doi:10.1007/BF00378907

Abstract

In the field, photosynthesis of Acer saccharum seedlings was rarely light saturated, even though light saturation occurs at about 100 μmol quanta m-2 s-1 photosynthetic photon flux density (PPFD). PPFD during more than 75% of the daylight period was 50 μmol m-2 s-1 or less. At these low PPFD's there is a marked interaction of PPFD with the initial slope (CE) of the CO2 response. At PPFD-saturation CE was 0.018 μmol m-2 s-1/(μl/l). The apparent quantum efficiency (incident PPFD) at saturating CO2 was 0.05–0.08 mol/mol. \({\text{CO}}_{2^ - }\) and PPFD-saturated CO2 exchange was 6–8 μmol m-2 s-1. The ratio of internal CO2 concentration to external (Ci/Ca) was 0.7 to 0.8 except during sunflecks when it decreased to 0.5. The decrease in Ci/Ca during 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 CO2 exchange 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%.

List of symbols

A

measured photosynthetic rate under any set of conditions (μmol m-2 s-1)

Am (atm)

measured photosynthetic rate at saturating PPFD, 350 μl/l CO2 and 21% (v/v) O2 (μmol m-2 s-1)

C

constant in equation of Smith (1937, 1938)

Ca

CO2 concentration in the air (μl/l)

Ci

CO2 concentration in the intercellular air space (μl/l)

Ci/*

Ci corrected for CO2 compensation point, i.e., Ci-I*, (μl/l)

CE

initial slope of the CO2 response of photosynthesis (μmol m-2 s-1/(μl/l))

CEM

CE at PPFD saturation

E

transpiration rate (mmol m-2 s-1)

F

predicted photosynthetic rate (μmol m-2 s-1)

G

leaf conductance to H2O (mol m-2 s-1)

I

photosynthetic photon flux density (μmol m-2 s-1)

N

number of data points

Pm

predicted photosynthetic rate at saturating CO2 and given PPFD (μmol m-2 s-1)

Pml

predicted photosynthetic rate at saturating CO2 and PPFD (μmol m-2 s-1)

Rd

residual respiratory rate (μmol m-2 s-1)

Ta

air temperature (°C)

Tl

leaf temperature (°C)

V

reaction velocity in equation of Smith (1937, 1938)

Vmax

saturated reaction velocity in equation of Smith (1937, 1938)

VPA

vapor pressure of water in the air (mbar/bar)

VPD

vapor pressure difference between leaf and air (mbar/bar)

X

substrate concentration in equation of Smith (1937, 1938)

α

initial slope of the PPFD response of photosynthesis at saturating CO2 (mol CO2/mol quanta)

α (atm)

initial slope of the PPFD response of photosynthesis at 340 μl/l CO2 and 21% (v/v) O2 (mol CO2/mol quanta)

I*

CO2 compensation point after correction for residual respiration (μl/l)

Λ

PPFD compensation point (μmol m-2 s-1)

Copyright information

© Springer-Verlag 1985

Authors and Affiliations

  • J. A. Weber
    • 1
  • T. W. Jurik
    • 1
  • J. D. Tenhunen
    • 1
  • D. M. Gates
    • 1
  1. 1.Biological Station and Botanical GardensUniversity of MichiganAnn ArborUSA
  2. 2.Lehrstuhl für Botanik II der Universität WürzburgWürzburgFederal Republic of Germany