Topography Dependence of Terrestrial Litter‐Derived Soil Respiration

Carbon (C) released from decomposing plant litter constitutes a major component of soil CO 2 efflux at the land surface, yet its contribution is rarely constrained separately from heterotrophic respiration of stable soil organic matter in global C budgets and Earth system model evaluations. We combined a global dataset with high‐resolution field observations to quantify the contribution of litter‐derived soil respiration ( R s ) using litter‐input and litter‐removal experiments, and to project its current distribution and future dynamics with machine‐learning models. On average, litter‐derived R s accounted for 30.9% of total R s . Higher contributions were estimated for experiments of shorter duration, highlighting the important role of fast‐cycling C alongside soil organic matter turnover. Litter‐derived R s varied substantially among ecosystems (grasslands > croplands > forests > wetlands) but did not differ significantly between tropical and temperate climates. Land surface slope exerted a stronger control than climatic or edaphic factors across both mountain and non‐mountain regions, suggesting a pronounced topographic regulation. High‐frequency field measurements further confirmed this pattern, with litter‐derived R s at mountain ridges being 1.5 times that in valleys. Global projections indicated a higher litter‐derived R s at low latitudes and greater vulnerability in cold climates under SSP 1–2.6 and SSP 5–8.5 scenarios. These findings demonstrate that litter decomposition is a substantial source of soil CO 2 flux that is strongly controlled by terrain. Accounting for this CO 2 pathway improves our understanding of how landscape heterogeneity influences terrestrial C cycle and enhances future predictions of ecosystem responses to climate change.