Dynamics of Soil CO₂ and CO₂ Efflux in Arid Soil

Soil carbon dioxide (CO₂) is an important component in the terrestrial ecosystem and regulates the atmosphere–land CO₂ exchange. Studying the variation of CO₂ in soil profile and surface CO₂ efflux can improve our understanding of the carbon cycle in the terrestrial ecosystem. In this paper, we analyze the dynamics of soil CO₂ and CO₂ efflux in an arid region, Yanqi, northwest China. Both CO₂ concentration and surface CO₂ efflux showed a clear seasonal variation, with two peaks in summer and a gradual decrease in autumn. We found that surface CO₂ efflux was exponentially related to soil temperature and linearly related to moisture when soil moisture was less than ~22%. We estimated surface CO₂ efflux by linear regression of CO₂ fluxes that were calculated by gradient method using Penman (1940), Marshall (1959), and Moldrup et al. (2013) models and found that the Marshall (1959) model did a better job than the other two models. However, there were considerable mismatches between the observation and model results. Our study indicates that the relationship is complex between the concentration of CO₂ in soil profile and surface CO₂ efflux in the arid region.