Investigating soil and atmospheric plant water stress using physiological and micrometeorological data

The effect of drought on the parameters of commonly used models of plant stomatal conductance is investigated, based on a large number of data obtained at the leaf level by plant physiologists, and at the canopy level by micrometeorologists. Sixty-three case studies are analysed in order to understand the intra- and inter-specific variations of the conductance and photosynthesis parameters in both stressed and unstressed conditions. It appears that the intraspecific variability is as large as the interspecific variability, and that the stomatal sensitivity to air humidity may depend on soil water content. Soil resistance to rooting seems to be an important factor of the variability. Field studies are consistent with leaf-scale ones. A simple representation of these effects is implemented into an interactive vegetation model and then applied to simulate three annual vegetation cycles on a fallow site.