Partitioning soil and air temperature warming effects on soil organic carbon storage

Soil organic carbon (SOC) storage is larger than organic carbon stored in the plant and atmosphere combined, prompting interest in understanding how SOC storage respond to rising temperatures. However, the consequences of warming in regulating SOC storage are still debated, with negative, positive, and non-significant responses reported. Most existing studies focusing on SOC responses to warming manipulate either air temperature or soil temperature, although in a realistic future air warming and soil warming co-occur. Based on results of meta-analysis and numerical simulations with a mechanistic model (T&C), we separate the effects of air warming, soil warming, and whole-ecosystem warming (combination of air warming and soil warming) on SOC storage. Results shows that soil warming alone decreases SOC storage due to temperature-driven increases in decomposition. Compared with soil warming, air warming has a more complex role. Air warming can cause water stress and hence a lower net primary productivity, as well as indirectly increase soil temperature. These factors tend to decrease SOC storage. However, in certain climates air warming can stimulate net primary production and decrease soil moisture limiting SOC decomposition. Once the latter mechanisms dominate, the SOC storge can increases with air warming. Our study helps refine the understanding and quantification of SOC responses in a warming climate.