title: Impact of mesophyll diffusion on estimated global land CO2 fertilization.
abstract: In C3 plants, CO2 concentrations drop considerably along mesophyll diffusion pathways from substomatal cavities to chloroplasts where CO2 assimilation occurs. Global carbon cycle models have not explicitly represented this internal drawdown and therefore overestimate CO2 available for carboxylation and underestimate photosynthetic responsiveness to atmospheric CO2. An explicit consideration of mesophyll diffusion increases the modeled cumulative CO2 fertilization effect (CFE) for global gross primary production (GPP) from 915 to 1,057 PgC for the period of 1901-2010. This increase represents a 16% correction, which is large enough to explain the persistent overestimation of growth rates of historical atmospheric CO2 by Earth system models. Without this correction, the CFE for global GPP is underestimated by 0.05 PgC/y/ppm. This finding implies that the contemporary terrestrial biosphere is more CO2 limited than previously thought.
authors.affiliation: Department of Geological Sciences, University of Texas at Austin, Austin, TX 78712;
authors.forename: Ying
authors.initials: Y
authors.lastname: Sun
authors.affiliation: Environmental Sciences Division and Climate Change Science Institute, Oak Ridge National Laboratory, Oak Ridge, TN 37831; lianhong-gu@ornl.gov robted@jsg.utexas.edu.
authors.forename: Lianhong
authors.initials: L
authors.lastname: Gu
authors.affiliation: Department of Geological Sciences, University of Texas at Austin, Austin, TX 78712; lianhong-gu@ornl.gov robted@jsg.utexas.edu.
authors.forename: Robert E
authors.initials: RE
authors.lastname: Dickinson
authors.affiliation: Environmental Sciences Division and Climate Change Science Institute, Oak Ridge National Laboratory, Oak Ridge, TN 37831;
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Norby
authors.affiliation: Department of Forestry, University of Missouri, Columbia, MO 65211; and.
authors.forename: Stephen G
authors.initials: SG
authors.lastname: Pallardy
authors.affiliation: Climate Change Science Institute and Computational Earth Sciences Group, Oak Ridge National Laboratory, Oak Ridge, TN 37831.
authors.forename: Forrest M
authors.initials: FM
authors.lastname: Hoffman
mesh_terms: D001272:Atmosphere; D002245:Carbon Dioxide / Q000737:chemistry / Q000378:metabolism*; D002736:Chloroplasts / Q000378:metabolism*; D008962:Models, Theoretical; D010944:Plants / Q000378:metabolism*
chemical_list: D002245:Carbon Dioxide
keywords: CO2 fertilization; carbon cycle; gross primary production; mesophyll conductance; photosynthetic model