Calculation of the specific rate of catabolic activity (Ac) from the heat flow rate of soil microbial reactions measured by calorimetry: significance and applications.

The calculation of parameters involved in the kinetics of the microbial soil reactions linked to the carbon cycle is strongly limited by the methodologies employed. Hence, a mathematical model is proposed to quantify easily the specific rate of catabolic activity A(c) by microcalorimetry based on Belaich's model. It permits to quantify A(c) from the plots of the heat flow rate vs. time recorded from soil samples amended with glucose. It was applied for several soil samples collected in the Amazon. The results obtained were compared, and statistical and graphical analyses were used to provide the biophysical significance of A(c) in soils. Results suggest that A(c) could be used as an empirical measure of stress. It correlates positively with the heat yield, Y(Q/X), of the soil microbial growth reactions, indicating that higher specific rates of catabolic activity cause higher dissipation of energy per unit of cell, yielding less-efficient metabolic reactions, which could affect negatively the soil quality. It is strongly affected by the initial microbial population and by the percentage of nitrogen in the samples. The statistical analysis also demonstrated that A(c) is more sensitive to changing environmental conditions than Y(Q/X), yielding more-accurate information about the soil metabolic processes.