at the time of the second peak (80 h) was around X = 608 g g−1with respect to the value at the first peak. These results confirm that yeast inhibited some of the soil microbiota or perhaps inhibitedthe establishment of new microorganisms as occurred with NYS.By using the semilogarithmic equation of exponential microbialgrowth, the increase in biomass could be calculated and thus, com-pared with those values determined by direct measurement of CO2.The increase in biomass, X = 787 ± 70 g g−1and 690 g g−1cal-culated for the first (NYS and YS) and second (NYS) peak of newlycollected soils, were not significantly different from the directlydetermined values.The calorespirometric ratio, p/rCO2between the basal specificthermal power and the specific rate of CO2evolution of soil with-out glucose gives a measure of the mineralizing activity of themicroorganisms, and equivalent to the metabolic quotient, qCO2,determined by conventional methods [21]. The calculated val-ues were 335 ± 12 and 199 ± 23 kJ mol−1for YS collected in 2011and 2012, respectively. Values of p/rCO2for NYS were 245 ± 7 in2011 and 249 ± 67 kJ mol−1in 2012. The latter value is not signifi-cantly different from that of YS collected in 2012. Values of p/rCO2between 250 and 460 kJ mol−1indicate aerobic degradation of car-bohydrates [17] and thus, it is evident that NYS and YS (2012) showhigh mineralizing activity with low waste of heat (low p). Yeastdecreased the mineralizing activity of the soil microbiota in 2011.Fig. 3C and D show values of p/rCO2calculated after the additionof glucose and in this case, these values are a measure of the carbonconversion efficiency of glucose into biomass by the microorgan-isms contained in the soils. Differences are observed between thesoils. The most remarkable is that NYS (Fig. 3D) shows values ofp/rCO2of 415 ± 49 kJ mol−1during peak time (Fig. 2) whereas thecalculated value for YS (Fig. 3C) is 518 ± 25 kJ mol−1indicating againa greater efficiency to convert glucose into biomass by microorgan-isms of NYS.A straight line is obtained when values of log SMB are plot-ted against log p, Fig. 4. Values of SMB were only calculated inthose cases where aerobic growth was present, i.e. when values ofp/rCO2were above 250 kJ mol−1. Values of SMB in curve ‘a’ of Fig. 4