Simulating short-term dynamics of non-increasing soil respiration rates by a model using Michaelis-Menten kinetics

Short-term dynamics of soil respiration rates over time measured at hourly intervals during less than 12 h after microbial substrates were added to soils can be classified into first-order, zero-order and growth-associated types. To simulate the zero-order type respiration rates, a model using Michaelis-Menten kinetics is proposed, because this kinetics model includes a maximum respiration rate but no increase in microbial biomass. In this model, soil respiration by microorganisms was assumed to be the sum of the mineralization of easily available substrates (R), which include both added glucose (G) and substrates released by disturbance such as a mixing treatment (D) and constant mineralization under steady state conditions. By analyzing the short-term dynamics of previously published respiration rates for a Kazakh forest, a Japanese forest and a Japanese arable soils, none of which show any increase with time, the parameter values of z(r) and D(0), which indicate the ratio of respired to utilized R and the initial concentration of D, respectively, were estimated. This allowed simulation of the decreasing concentrations of R and estimation of the parameters V(max) and K(M) in the Michaelis-Menten equation. Simulations using the obtained parameter values matched the measured data well. Correlation coefficients (r2) and root mean square errors (RMSE) indicated that the simulations usually matched the measured data, which included not only zero-order respiration rates but also first-order respiration rates. Therefore, the proposed model using Michaelis-Menten kinetics can be used to simulate the short-term dynamics of respiration rates, which show no increase over time, when easily available substrates would be added in soils.