Articles | Volume 13, issue 20
Atmos. Chem. Phys., 13, 10243–10269, 2013
Atmos. Chem. Phys., 13, 10243–10269, 2013

Research article 22 Oct 2013

Research article | 22 Oct 2013

Photosynthesis-dependent isoprene emission from leaf to planet in a global carbon-chemistry-climate model

N. Unger1, K. Harper1, Y. Zheng2, N. Y. Kiang3, I. Aleinov3, A. Arneth4, G. Schurgers5, C. Amelynck6, A. Goldstein7, A. Guenther8, B. Heinesch9, C. N. Hewitt10, T. Karl11, Q. Laffineur9,18, B. Langford12, K. A. McKinney13, P. Misztal7, M. Potosnak14, J. Rinne15, S. Pressley16, N. Schoon6, and D. Serça17 N. Unger et al.
  • 1School of Forestry and Environmental Studies, Yale University, New Haven, CT 06511, USA
  • 2Department of Geology and Geophysics, Yale University, New Haven, CT 06511, USA
  • 3NASA Goddard Institute for Space Studies, New York, NY 10025, USA
  • 4Karlsruhe Institute for Technology, Institute of Meteorology and Climate Research, Kreuzeckbahnstr. 19, 82467 Garmisch-Partenkirchen, Germany
  • 5Department of Earth and Ecosystem Sciences, University of Lund, Lund, 22362, Sweden
  • 6Belgian Institute for Space Aeronomy, Ringlaan-3-Avenue Circulaire, 1180 Brussels, Belgium
  • 7Department of Environmental Science, Policy, and Management, University of California at Berkeley, Berkeley, CA 94720, USA
  • 8National Center for Atmospheric Research, Boulder, CO, USA
  • 9Unité de Physique des Biosystèmes, Gembloux Agro-Bio Tech, University of Liège, Gembloux, Belgium
  • 10Lancaster University, Bailrigg, Lancaster, UK
  • 11University of Innsbruck, Institute of Meteorology and Geophysics, Innsbruck
  • 12Centre for Ecology and Hydrology, Midlothian, UK
  • 13Department of Chemistry, Amherst College, Amherst, Massachusetts, USA
  • 14DePaul University, Chicago, IL, USA
  • 15University of Helsinki, Helsinki, Finland
  • 16Washington State University, Pullman, WA, USA
  • 17Université Toulouse, Toulouse, France
  • 18Royal Meteorological Institute of Belgium, Ringlaan-3-Avenue Circulaire, 1180 Brussels, Belgium

Abstract. We describe the implementation of a biochemical model of isoprene emission that depends on the electron requirement for isoprene synthesis into the Farquhar–Ball–Berry leaf model of photosynthesis and stomatal conductance that is embedded within a global chemistry-climate simulation framework. The isoprene production is calculated as a function of electron transport-limited photosynthesis, intercellular and atmospheric carbon dioxide concentration, and canopy temperature. The vegetation biophysics module computes the photosynthetic uptake of carbon dioxide coupled with the transpiration of water vapor and the isoprene emission rate at the 30 min physical integration time step of the global chemistry-climate model. In the model, the rate of carbon assimilation provides the dominant control on isoprene emission variability over canopy temperature. A control simulation representative of the present-day climatic state that uses 8 plant functional types (PFTs), prescribed phenology and generic PFT-specific isoprene emission potentials (fraction of electrons available for isoprene synthesis) reproduces 50% of the variability across different ecosystems and seasons in a global database of 28 measured campaign-average fluxes. Compared to time-varying isoprene flux measurements at 9 select sites, the model authentically captures the observed variability in the 30 min average diurnal cycle (R2 = 64–96%) and simulates the flux magnitude to within a factor of 2. The control run yields a global isoprene source strength of 451 TgC yr−1 that increases by 30% in the artificial absence of plant water stress and by 55% for potential natural vegetation.

Final-revised paper