COMPARISON OF 4 METHODS FOR MEASURING RESPIRATION IN ORGANIC MATERIAL

Four methods for measurement of respiration (CO2 evolution) were compared on uniformly prepared, birch forest-floor organic matter; the methods included infrared gas analysis (i.r.g.a.), gas chromatography (g.c.), KOH absorption of CO2 (b.a.) and the Gilson respirometer. Respiration estimates were made at a single temperature and also at variable temperatures at constant moisture contents. The i.r.g.a. and b.a. methods gave maximum estimates for respiration; the g.c. gave lowest, with the Gilson intermediate. Lower estimates for the g.c. are attributed to the closed system employed, which included no means of increasing gas diffusion (such as a KOH-CO2 sink or continuous gas flow) out of the sample into the unoccupied space of the respiration chamber. At 25°C, the minimum sensitivity of the g.c. and Gilson were 3.8 and 3.6 μg CO2, respectively. The minimum sensitivity of the b.a. method (44 μg CO2) could have been improved with use of a micro-liter burette for titrations. The least minimum sensitivity, 0.31 μg CO2, was attained with the i.r.g.a. Conditions under which any of the techniques may be used to estimate respiration should be carefully worked out. The relationship between sample size, gas flow rate (open system), chamber atmosphere composition (closed system), and chamber design should be established with sufficient confidence so that stimulation of respiration by excessive gas flow rate, or exhaustion of O2 or CO2 inhibition through extended chamber closure does not adversely affect respiration estimates. © 1979.