Validation of the traditional calorespirometric procedure using external respirometry to quantify the calorespirometric ratio of soil microbial metabolism

The calorespirometric ratio is a metabolic indicator that can be useful in soil science for understanding thermodynamics and the carbon use efficiency of soil microbial metabolism. Calculating calorespirometric ratios for soil microbial metabolism involves the development of calorespirometric procedures using calorimeters of the heat conduction type. The calorespirometric measurements for soil microbial metabolism are recent and their calculation requires sensitive calorimeters and accurate measurements. Their interpretation for soils has been developing during the last years, but accuracy of the methods involved in their calculation are still under question. This paper analyses the precision of the traditional calorespirometric method to yield these calorespirometric ratios by comparison with analysis of respiration measured in parallel using chromatography. Results indicated that the CO₂ data obtained by chromatography and calorespirometry are significantly correlated with each other and with the heat rate of the soil microbial metabolism. The comparison of the CO₂ data from both methods by the paired sample Wilcoxon signed rank test yielded no statistically significant differences. Nevertheless, small changes in the CO₂ determinations, due to the method of measurement or to the reproducibility of these indices in the soil replicates, affected the experimental quantitative values of the calorespirometric ratios. Differences in the quantitative values were large enough in some of the samples to yield distinct interpretations of the results.