Implications of non-uniform stomatal closure on gas exchange calculations

Abstract. This paper discusses the consequences of non-uniform (= patchwise) stomatal closure on the estimation of gas exchange parameters. The estimation of the partial pressure of internal CO₂ (c_i) appears to be little sensitive to complete non-uniform stomatal closure. During the process of closure of these patches, however, a lower c_i will be calculated. For gas exchange measurements done at low wind speeds, it can be shown that an error is made in the partitioning of the total vapour transfer resistance into boundary layer and stomatal resistance. This error influences the calculated total transfer resistance of gases other than water vapour (e.g. CO₂). The apparent negative internal gas concentrations that have sometimes been found in fumigation experiments with SO₂ can possibly be explained by this error.