A one-compartment model to study soil carbon decomposition rate at equilibrium situation

Based on world-wide observed soil carbon density data and model-simulated net primary production (NPP), we obtained a one-compartment model directly calculating average soil carbon respiration rate and soil carbon density at equilibrium situation. Our formulation shows that the average decomposition rate of soil organic matter, both at dry and wet soil condition, is particularly sensitive to moisture/precipitation changes and it is also sensitive to temperature. The data show that, at wet soil condition, decomposition rate decreases with moisture increasing, while at dry soil condition, it increases with moisture increasing. These results are consistent with previous studies. The temperature effect on soil respiration rate is evident, with Q10=1.7. The model has a good resolution to describe soil carbon densities at various vegetation types in the Holdridge life ecosystem classification system. Results show that the highest soil carbon densities occur in rain forest/tundra, while the lowest values in deserts and the highest soil respiration rates occur in wet forest/tundra but not in rain forest/tundra, while the lowest rates occur in desert. The calculated present terrestrial carbon pool is ≈1200 PgC. On the basis of model results, some recent conclusions indicating that soil organic carbon decomposition does not vary with temperature should be revised. The soil respiration rates are highly dependent on the combined effects of temperature and precipitation, but not any individual effect. High precipitation rate or soil moisture will greatly prevent soil organic matter from decomposition.