Spatial and temporal variations of soil CO₂ efflux from heterotrophic respiration and straw decomposition in the North China Plain over 2003-2024: process-based model

Understanding the spatial and temporal variations of soil CO₂ efflux from heterotrophic respiration (HR) and straw decomposition (SDR) is essential for constraining cropland carbon budgets, yet long‑term assessments that distinguish these sources remain limited. Here, we developed process‑based models for HR and SDR using multi‑site field observations. The models were then applied across the North China Plain under the winter wheat–summer maize rotation system, driven by high‑resolution forcing data to generate 1 km, 8‑day simulations for 2003–2024. Validation with independent data showed high consistency between simulations and observations (HR: R² = 0.97; SDR: R² > 0.93). Average CO₂ efflux from HR and SDR was estimated at 505.5 ± 34.5 and 278.0 ± 84.5 g C m⁻² yr⁻¹, respectively. HR exhibited a pronounced latitudinal gradient, driven primarily by SOC content, whereas SDR showed a more gradual decline toward higher latitudes, associated with straw return amounts. Both fluxes peaked in summer, but HR displayed a substantially larger seasonal amplitude. Interannual HR increased significantly across the region (4.6 g C m⁻² yr⁻¹), largely in response to rising temperatures. SDR showed no significant trend before 2010 but increased sharply thereafter (9.3 g C m⁻² yr⁻¹), driven mainly by rising straw inputs following regional straw incorporation policies. The contribution of SDR to total soil CO₂ efflux increased from 27% in 2003–2010 to 39% in 2011–2024, highlighting the need to better account for residue‑derived CO₂ when evaluating cropland carbon processes. Collectively, the findings clarify how climate and management interact to regulate cropland CO₂ emissions and strengthen the process basis for agricultural carbon modeling.