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

Abstract

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 CO2 efflux and soil-air CO2 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 CO2 in soil layers originated from root and microbial respiration, which were assumed to depend on soil temperature and moisture multiplicatively. The CO2 flux between the layers was driven by diffusion, which depended on CO2 concentration, porosity, and temperature of the layers. The model predictions of CO2 effluxes and soil CO2 concentrations were close to those observed in the field. There was a clear seasonal pattern in the soil CO2 efflux and the soil-air CO2 concentration. According to the model analysis, most of the CO2 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 CO2 concentration was strongly dependent on factors affecting the diffusion properties of the soil, that is, the soil porosity and the soil-water content. The CO2 efflux and the soil-air CO2 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 CO2 efflux and CO2 concentration.