A Process‐Based Model for Predicting Soil Carbon Dioxide Efflux and Concentration

Decomposition and root respiration processes, important to C cycling in terrestrial ecosystems, are affected by soil temperature, soil moisture, and other soil properties. For studying the effect of these factors on soil CO 2 efflux and soil‐air CO 2 concentration, a dynamic model was developed. In the model, soil was described in successive layers and the processes and soil properties were described separately for each layer. The CO 2 in soil layers originated from root and microbial respiration, which were assumed to depend on soil temperature and moisture multiplicatively. The CO 2 flux between the layers was driven by diffusion, which depended on CO 2 concentration, porosity, and temperature of the layers. The model predictions of CO 2 effluxes and soil CO 2 concentrations were close to those observed in the field. There was a clear seasonal pattern in the soil CO 2 efflux and the soil‐air CO 2 concentration. According to the model analysis, most of the CO 2 was produced in the humus layer throughout the year, but the contribution of deeper layers to total respiration was higher in winter than in summer. The CO 2 concentration was strongly dependent on factors affecting the diffusion properties of the soil, that is, the soil porosity and the soil‐water content. The CO 2 efflux and the soil‐air CO 2 concentration were overestimated, if the soil‐water content was not included in the soil respiration model. The model developed in this study provided a simple and an effective tool for studying the factors affecting soil CO 2 efflux and CO 2 concentration.