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 CO2 concentration (Cs) or leaf intercellular CO2 concentration (Ci), 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 Cs performed slightly better than the models applying Ci. 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 Cs or Ci were brought forward and discussed.