2.5. Calorimetric analysis
A twin heat conduction calorimeter (Lund University, Sweden)was used [12,13]. Soil samples (3.0–4.0 g dw) were stabilized during 7 days at 25◦C in a polyethylene bag at a water content equiv alentto 60% of FCH. Then, an appropriate amount of water containing glu-cose as to get FCH and the required amount of the carbon source wasadded. The soil was thoroughly mixed by hand and the equivalent of1.0–1.5 g (dw) was weighed into the calorimeter ampoule (8.0 cm3).The ampoule was hermetically closed and after the 30 min needed to equilibrate the calorimetric system, thermal power (P) – time(t) curves of microbial growth were recorded at 25◦C. An ampoulecontaining 1 g of agar was used as reference. Microsoft Excel 2007(Microsoft corporation) and Origin 6.0 (Microcal, Inc.) were used toconvert the curves obtained into mass specific thermal power (p) –time (t) curves and integrated to obtain the specific heat (q) asso-ciated with the glucose degradation. From the semi-logarithmicconversion of the portion of the curve that indicates exponentialmicrobial growth (log p = log p0+ t) the microbial growth rate con-stant, , was calculated. To determine the enthalpy change due tometabolism the expression mH = (q/m) 180.16 was used where mis the amount of glucose used and 180.16 is the molecular weightof glucose. In turn, mH results from an enthalpy change due tocatabolism,