@Article{Sun_PNAS_20141104,
 author		= {Ying Sun and Lianhong Gu and Robert E. Dickinson and Richard J. Norby and Stephen G. Pallardy and Forrest M. Hoffman},
 title		= {Impact of Mesophyll Diffusion on Estimated Global Land {CO$_2$} Fertilization},
 journal	= PNAS,
 volume		= 111,
 number		= 44,
 pages		= {15774--15779},
 doi		= {10.1073/pnas.1418075111},
 day		= 4,
 month		= nov,
 year		= 2014,
 abstract	= {In C3 plants, CO$_2$ concentrations drop considerably along mesophyll diffusion pathways from substomatal cavities to chloroplasts where CO$_2$ assimilation occurs. Global carbon cycle models have not explicitly represented this internal drawdown and therefore overestimate CO$_2$ available for carboxylation and underestimate photosynthetic responsiveness to atmospheric CO$_2$. An explicit consideration of mesophyll diffusion increases the modeled cumulative CO$_2$ 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 CO$_2$ 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 CO$_2$ limited than previously thought.}
}