Examination of the method for measuring soil respiration in cultivated land: Effect of carbon dioxide concentration on soil respiration

An acceleration of soil respiration with decreasing CO 2 concentration was suggested in the field measurements. The result supporrs that obtained in laboratory experiments in our previous study. The CO 2 concentrations in a chamber of the alkali absorption method (the AA‐method) were about 150–250 parts/10 6 lower than that in the atmosphere (about 350 parts/10 6 ), while those observed in the open‐flow IRGA method (the OF‐method) were nearly equal to the soil surface CO 2 levels. The AA‐method at such low CO 2 levels in the chamber appears to overestimate the soil respiration. Our results showed that the rates obtained by the AA‐method were about twice as large as those by the OF‐method in field and laboratory measurements. This finding has important consequences with respect to the validity of the existing data obtained by the AA‐method and the estimation of changes in the terrestrial carbon flow with elevated CO 2