Stomatal conductance - gs
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"Stomatal condcutance maximum is a numerical measure of the maximum rate of passage of either water vapour or carbon dioxide through the stomata, or small pores of the plant." (TEMS)
matal conductance gs plays an important role in the plant-atmosphere water exchange and hence it is a key parameter in many ecological models (Chen et al., 1999). Diffusion of CO2 into the mesophyll of leaves and water vapour from the leave to the atmosphere is mainly driven by the stomatal aperture, which is controlled by a complex system of plant physiological processes. Nearly all the water transpired by plants is lost through the stomata as water vapour diffusion via cuticle can be neglected. Methods applied for determining the diffusive conductance include porometer and photosynthesis cuvette measurements as well as energy balancing approaches.
Published data are somehow difficult to compare as investigations under natural conditions are strongly affected for instance by water vapour pressure deficit, soil moisture, general conditions of the plant (healthy/unhealthy), position of leaves or needles (shaded/exponated), age of leaves or needles. Nevertheless, many ecological models need single gs values as input parameters.
Stomatal conductance is given in [mm s-1]. In cases where stomatal conductance is published in [mmol m-2 s-1] values are divided by 41 for transformation according to Körner (1979, calculation based on 293 K and 105 Pa). Many data are taken as published or read of graphs.
Körner et al. (1979) provided a comprehensive review. Additional values for stomatal conductance according to typical plant species in temperate land use systems evaluated by other authors are taken into account supplementary.