What Regulates Soil CO2 Concentrations? A Modeling Approach to CO2 Diffusion in Deep Soil Profiles

About 10% of the CO2 in the above-ground atmosphere is annually recycled back to the atmosphere from the soil. Soil respiration (the sum of root and microbial respiration) increases soil CO2 concentrations by 10- to 100-fold or more than that in the above-ground atmosphere, and such elevated concentrations have a variety of significant effects on soil systems. Because increased soil respiration is expected to result from future global climates, due both to elevated atmospheric CO2 and temperature, we developed a multibox model without steady-state assumptions to investigate the factors that regulate soil CO2 concentrations. Results suggest that below-ground CO2 concentrations are predominantly controlled by tortuosity of pores, depth distributions of root and microbial activity, and total production of soil CO2. Considering the dependence of soil respiration rates on climate, our results are significant in suggesting that future climate change will increase soil CO2 concentrations in direct proportion to increases of below-ground respiration.