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 CO2 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 (Rn) is constant at various CO2 concentrations, at least in a short term, k_CO2 should be the value that makes the leak-corrected Rn 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 Rn at various CO2 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 CO2 concentrations inside and outside the chamber based on thermally killed leaves at various flow rates. Furthermore, the present approach does not require the ambient CO2 concentration outside the chamber (Ca) if Ca in the laboratory is stable, which provides a feasible way to correct the photosynthetic rate, taking diffusional leakage into account.