Exchange of carbon dioxide between vegetation and the atmosphere
Abstract Carbon dioxide is transported from the atmosphere to leaf surfaces very efficiently, and atmospheric diffusion resistances rarely affect photo-synthetic rates by more than 10%. The largest single resistance is in the boundary layer of individual leaves, and this is a well-known function of leaf size, wind speed, and leaf to air temperature difference. For uniform vegetative canopies a fully turbulent boundary layer exists above; this layer is also well understood and well-proven equations can be used to relate the carbon dioxide flux to the concentration gradient. Transport in the air within and just above vegetative canopies is less well understood. Turbulent diffusion theory has been shown to be inadequate, and consequently the diffusion resistance analogy cannot be used. Recent work, however, shows that Lagrangian theories of dispersion offer an alternative and more accurate description of transport within canopies.