A comparison of photosynthesis-dependent stomatal models using twig cuvette field data for adult beech (Fagus sylvatica L.)

Six photosynthesis-dependent stomatal models were tested and compared against twig cuvette gas exchange data for adult common beech ( Fagus sylvatica L.). The models differed in the use of (1) either leaf surface CO 2 concentration ( C s ) or leaf intercellular CO 2 concentration ( C i ), and of (2) either measured environmental humidity variables or a crudely calculated leaf water potential to simulate the effect of drought stress on stomatal conductance. The models applying C s performed slightly better than the models applying C i . The models based on environmental humidity variables performed distinctly better than the models applying a calculated leaf water potential. Several explanations for the observed performance differences between models applying C s or C i were brought forward and discussed.