Canopy stomatal conductance

Stomata are major conduits for the diffusion of many trace gas species between leaves and the atmosphere. The role of the stomata on controlling gas exchange between the terrestrial biosphere and the atmosphere at the landscape, meso- and global-scales has only recently been recognized. Further advances in modelling large-scale trace gas exchange will depend on our ability to understand and model stomatal mechanics at the scale of the pertinent sub-unit, which is typically that of the canopy. This paper describes two approaches for estimating canopy stomatal conductance. One approach is based on 'bottom-up' scaling. This approach computes canopy stomatal conductance by integrating detailed leaf-level and environmentally-driven, physiological processes with the use of a detailed canopy micrometeorology model. The other approach is based on 'top-down' scaling. It interprets the integrated canopy stomatal conductance from measured fluxes of trace gas exchange. Frameworks for extending these scaling approaches to non-idea conditions are given. 96 refs., 5 figs.