A kinetic parameter describing soil available carbon and its relationship to rate increase in C mineralization

No standard rapid method reliably assesses the potential energy supply to soil microorganisms. We found that the metabolic quotient qCO2 failed to adequately reflect repeated weekly glucose-C additions corresponding to 25 and 50% of soil respiratory CO2C loss. We addressed the concept of an available C pool in soil using a kinetic parameter (AC) derived from a modified Michaelis-Menten equation. The new parameter AC correlates significantly and positively to soil microbial biomass, to the Michaelis constant and negatively to the initial potential rate of increase in C mineralization (R0). A negative correlation between the AC-to-biomass ratio, which we have called the specific C reserve (SCR), and R0 was found to be highly significant (P < 0.001). The qCO2 of soil microorganisms did not correlate significantly (P > 0.05) with any of the indices discussed. Based on its theoretical soundness, its correlative value and its applicability to realistic soil-plant systems, we propose that AC becomes a standard measure of the available C pool in soil.