Separation of root and microbial respiration: Comparison of three methods

In a laboratory experiment, the following methods of separating the soil CO2 flux into the root respiration and the respiration of the rhizosphere and nonrhizosphere microorganisms were compared: (1) root exclusion, (2) component integration, and (3) 14C pulse labeling. Depending on the method used, the combined contribution of the rhizosphere microorganisms and roots varied from 18 to 40% of the total CO2 emission; the contribution of the roots alone was 8–19%, and that of the nonrhizosphere microorganisms was 51–82%. The nonisotope methods (1 and 2) gave similar results of the separation. The pulse labeling of plants satisfactorily separated the root and microbial respiration, but it is unsuitable for determining the respiration of the nonrhizosphere microorganisms. Advantages and disadvantages of each method are discussed.