Oscillatory behavior of two nonlinear microbial models of soil carbon decomposition

[摘要] A number of nonlinear models have recently been proposedfor simulating soil carbon decomposition. Their predictions of soil carbonresponses to fresh litter input and warming differ significantly fromconventional linear models. Using both stability analysis and numericalsimulations, we showed that two of those nonlinear models (a two-pool modeland a three-pool model) exhibit damped oscillatory responses to smallperturbations. Stability analysis showed the frequency of oscillation isproportional to √(ϵ⁻¹−1) K_s/V_s in the two-pool model, and to √(ϵ⁻¹−1) K_l/V_l in the three-pool model, where ϵ ismicrobial growth efficiency, K_s and K_l are the half saturationconstants of soil and litter carbon, respectively, and /V_s and /V_l arethe maximal rates of carbon decomposition per unit of microbial biomass forsoil and litter carbon, respectively. For both models, the oscillation has aperiod of between 5 and 15 years depending on other parameter values, and hassmaller amplitude at soil temperatures between 0 and 15 °C. Inaddition, the equilibrium pool sizes of litter or soil carbon areinsensitive to carbon inputs in the nonlinear model, but are proportional tocarbon input in the conventional linear model. Under warming, the microbialbiomass and litter carbon pools simulated by the nonlinear models canincrease or decrease, depending whether ϵ varies withtemperature. In contrast, the conventional linear models always simulate adecrease in both microbial and litter carbon pools with warming. Based onthe evidence available, we concluded that the oscillatory behavior andinsensitivity of soil carbon to carbon input are notable features in thesenonlinear models that are somewhat unrealistic. We recommend that a bettermodel for capturing the soil carbon dynamics over decadal to centennialtimescales would combine the sensitivity of the conventional models tocarbon influx with the flexible response to warming of the nonlinear model.

[学科分类] 地球化学与岩石