A practical approach to estimate diffusional leakages of leaf chamber of open gas exchange systems using intact leaves

We propose a novel approach to determine the coefficient of CO 2 diffusional leakage ( k _CO2 ) in the chamber of a portable open gas exchange system (Li‐6400, Li‐Cor Inc., NE, USA) using intact leaves. Assuming that dark respiration rate (R n ) is constant at various CO 2 concentrations, at least in a short term, k _CO2 should be the value that makes the leak‐corrected R n constant. We used 2 representative tree species native to northern Japan, Japanese white birch ( Betula platyphylla var. japonica ) and Japanese oak ( Quercus mongolica var. crispula ), to determine k _CO2 , by measuring R n at various CO 2 concentrations. Irrespective of the species, k _CO2 estimated by the present approach was well correlated with the diffusional leak coefficient ( k _flow ) estimated by the generally used approach that utilizes CO 2 concentrations inside and outside the chamber based on thermally killed leaves at various flow rates. Furthermore, the present approach does not require the ambient CO 2 concentration outside the chamber (C a ) if C a in the laboratory is stable, which provides a feasible way to correct the photosynthetic rate, taking diffusional leakage into account.