Modeling transient soil moisture limitations on microbial carbon respiration

Abstract. Observations show that soil microorganisms can survive periods of aridity and recover rapidly after wetting events. This behavior can be explained by a moisture-dependent adaptation (i.e. the ability to transition between a dormant state in dry conditions and an active state in wet conditions). Though this dynamic behavior has been previously incorporated into modeling frameworks, a direct comparison between a model application of this active-dormant transition mechanism and a more simplified first-order model has yet to be made. Here, we developed two models, one using simplified first-order kinetics and the other featuring a process-based rate expression incorporating the transition between active and dormant biomass. The two approaches are contrasted through a benchmarking exercise using a set of time series soil incubation datasets. We evaluated the two models using an Akaike Information Criterion (AIC). Combining the AIC evaluation and model-data comparison, we conclude that the dormancy-incorporated model performs better for shallow soils (above 108 cm), despite the added parameters required. In addition, this model is uniquely capable of reproducing transient CO₂ flux rates associated with dynamic microbial response to changing soil moisture. In contrast, the first-order model achieves better AIC scores when simulating the incubation data obtained from our deepest soils (112–165 cm). However, deep soils constitute a minor contribution to the overall CO₂ flux of an intact soil column. Thus, the dormancy-incorporated model may better simulate respiration of the whole soil.