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DIVISION S-1—SOIL PHYSICS

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

Dep. of Forest Ecology, P.O. Box 27, FIN-00014 University of Helsinki, Finland

^* Corresponding author (jukka.pumpanen{at}helsinki.fi)

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.

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