Vertical and seasonal variations in soil CO2 production in a 55-year-old oriental arborvitae (Platycladus orientalis) plantation in China

The aim of this work was to explore the vertical and seasonal variations of CO2 within the soil profile based on Fick's law of diffusion in an oriental arborvitae plantation. We continuously measured the soil CO2 concentration profile using CO2 sensors buried at different depths in a coniferous forest in northern China and calculated the CO2 flux based on the profile measurements using a dynamic model. The diurnal pattern of CO2 concentration and flux fluctuated during the day and varied less at night. The CO2 profile had a vertical gradient, with the highest concentrations in the deepest soil layers. The CO2 flux had a clear seasonal pattern with a maximum in summer and a minimum in winter. The contributions of the H, A, B, and C horizons to the total CO2 flux were 75.38, 13.52, 7.61, and 3.49%, respectively. Q(10) was 2.668, 4.469, 1.175, and 3.333 in the H, A, B, and C horizons, respectively. The CO2 flux determined from the concentration profiles agreed well with the CO2 flux measured by open dynamic chambers, suggesting that this model could be used to successfully measure soil CO2 emissions and to describe the processes underlying CO2 efflux.