Air and soil warming have different effects on soil organic carbon storage

Warming impacts both net primary production (NPP) and soil organic carbon (SOC) decomposition, and consequently, SOC storage. However, the role of warming in regulating SOC storage remains debated. Here, we leverage literature data of warming experiments and a mechanistic model to explore SOC responses to warming by partitioning the effects of air and soil warming. Both the literature data and numerical model show that air and soil warming play distinct roles in regulating SOC storage, with insignificant SOC responses under air warming and negative responses to soil warming. Soil warming decreases SOC storage because of temperature-driven increases in decomposition rate. Air warming effects on SOC are more complex. In some cases, air warming can lead to a lower NPP and higher decomposition rate. In others, air warming can stimulate NPP and enhance soil moisture depletion that inhibits SOC decomposition. Once the latter mechanisms dominate, SOC storage increases with air warming.