Evaluation of soil CO₂ production and transport in Duke Forest using a process‐based modeling approach

Soil surface CO 2 efflux is an important component of the carbon cycle in terrestrial ecosystems. However, our understanding of mechanistic controls of soil CO 2 production and transport is greatly limited. A multilayer process‐based soil CO 2 efflux model (PATCIS) was used to evaluate soil CO 2 production and transport in the Duke Forest. CO 2 production in the soil is the sum of root respiration and soil microbial respiration, and CO 2 transport in the soil mainly simulates gaseous diffusion. Simulated soil CO 2 efflux in the Duke Forest ranged from 5 g CO 2 m −2 d −1 in the winter to 25 g CO 2 m −2 d −1 in summer. Annual soil CO 2 efflux was 997 and 1211 g C m −2 yr −1 in 1997 and 1998, respectively. These simulations were consistent with the observed soil CO 2 efflux. Simulated root respiration contributed 53% to total soil respiration. Soil temperature had the dominant influence on soil CO 2 production and CO 2 efflux while soil moisture only regulated soil CO 2 efflux in the summer when soil moisture was very low. Soil CO 2 efflux was sensitive to the specific fine root respiratory rate and live fine root biomass. Elevated CO 2 increased annual soil CO 2 efflux by 26% in 1997 and 18% in 1998, due mainly to the enhanced live fine root biomass and litterfall. On a daily to yearly basis, CO 2 production is almost identical to CO 2 efflux, suggesting that CO 2 transport is not a critical process regulating daily and long‐term soil surface CO 2 effluxes in the Duke Forest. We also developed a statistical model of soil CO 2 efflux with soil temperature and moisture. Daily soil CO 2 efflux estimation by the statistical model showed a similar pattern to the simulated soil CO 2 efflux, but the total annual CO 2 efflux was slightly lower. While the statistical model is simple, yet powerful, in simulating seasonal dynamics of soil CO 2 efflux, the process‐based model has the potential to advance our mechanistic understanding of soil CO 2 efflux variations in the current and future worlds.