Atmos. Chem. Phys. Discuss., 13, 17717-17791, 2013
© Author(s) 2013. This work is distributed
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
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. Laffineur12, B. Langford13, K. A. McKinney14, P. Misztal7, M. Potosnak15, J. Rinne16, S. Pressley17, N. Schoon6, and D. Serça18
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
7Dept. of Environmental Science, Policy, and Management, University of California at Berkeley, Berkeley, CA 94720, USA
8National Center for Atmospheric Research, Boulder, CO, USA
9Université de Liège, Gembloux, Belgium
10Lancaster University, Lancaster, UK
11University of Innsbruck, Institute of Meteorology and Geophysics, Innsbruck, Austria
12Unité de Physique des Biosystèmes, Gembloux Agro-Bio Tech, University of Liège, Gembloux, Belgium
13Centre for Ecology and Hydrology, Midlothian, UK
14Department of Chemistry, Amherst College, Amherst, Massachusetts, USA
15DePaul University, Chicago, IL, USA
16University of Helsinki, Helsinki, Finland
17Washington State University, Pullman, WA, USA
18Université Toulouse, Toulouse, France

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 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 Tg C yr-1 that increases by 30% in the artificial absence of plant water stress and by 55% for potential natural vegetation.

Citation: Unger, N., Harper, K., Zheng, Y., Kiang, N. Y., Aleinov, I., Arneth, A., Schurgers, G., Amelynck, C., Goldstein, A., Guenther, A., Heinesch, B., Hewitt, C. N., Karl, T., Laffineur, Q., Langford, B., McKinney, K. A., Misztal, P., Potosnak, M., Rinne, J., Pressley, S., Schoon, N., and Serça, D.: Photosynthesis-dependent isoprene emission from leaf to planet in a global carbon–chemistry–climate model, Atmos. Chem. Phys. Discuss., 13, 17717-17791, doi:10.5194/acpd-13-17717-2013, 2013.
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