Interpretation of the metabolic enthalpy change, Delta H-met, calculated for microbial growth reactions in soils

The microcalorimetric method was used to calculate the metabolic enthalpy c hange per mol of glucose degraded by soil microorganisms, DeltaH(met). This parameter has been calculated by microcalorimetry for many organic, inorga nic and biochemical reactions, but there is only some information about its quantification for microbial growth reactions in soils. Values of DeltaH(m et) were calculated for different soil samples collected in Galicia (Spain) and Campinas (Sao Paolo, Brazil). Exponential microbial growth was stimula ted in all soil samples by the addition of glucose and power-time curves we re recorded. Results showed changes in the values of DeltaH(met) calculated for all the soil samples, suggesting a dependence of this value with the m icrobial growth rate constant, with the percentage of growth, with the init ial number of microorganisms of soil samples, with the quantity of glucose added and with the strain of bacteria growing in soil. The interpretation of variations of DeltaH(met) provides important qualitat ive and quantitative information. It reports data that allow to interpret f rom a qualitative point of view, the increase in biomass as a consequence o f the degradation of the organic matter in soil, to understand changes in t he percentages of soil organic matter and to know if the microbial populati on growing in differential soil samples is homogeneous. Therefore, to repor t that value would be very important in ecological studies, but beforehand, it is necessary to solve some problems that can appear in the experiments done to make the quantification.