Modelling the effects of soil water limitations on transpiration and stomatal regulation of cauliflower

Quantitative knowledge of the drought adaptation processes of crops is an important prerequisite for efficient irrigation management. To study the adaptation of stomatal resistance and transpiration of cauliflower to three different drought situations an experiment using containers with 220 l of soil volume was conducted with three different water supply regimes to obtain a wide variation of plant reactions in time and intensity. One model of transpiration and three models of stomatal conductance based on either soil water potential, leaf water potential, or root signals were developed and parameterised with the experimental data. Specific transpiration, i.e. transpiration per unit leaf area, could be well described with a model based on soil water potential, but the threshold water potential below which specific transpiration declined was dependent on the atmospheric evaporative demand, characterised by potential transpiration. Stomatal resistance of unstressed plants was dependent on the radiation environment, and the threshold soil water potential also increased with increasing atmospheric transpiration requirement. Models using leaf water potential or simulated stomatal closure based on xylem ABA concentration gave also satisfactory descriptions of the experimental data but had other shortcomings like high correlations between model parameters and difficult input requirements that limit their usefulness for the prediction of effects of water limitations.