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

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 (R_n ) is constant at various CO₂ 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 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 (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.