Fast Transit of Carbon Inputs in Global Soil Profiles Regardless of Entering Depth

Climate and land management changes are altering carbon inputs to soil. The consequence of such input changes on long-term soil organic carbon (SOC) balance depends on the transit behavior of carbon inputs. Using observational carbon input and radiocarbon data in global soil profiles, we reveal that on average nearly 25% of new entering carbon leave soil in 1 year irrespective of entering depth, and the remained fraction after 30 years is only similar to 13%. Nevertheless, the majority of SOC is older than 30 years in all soil depths. Together, these results demonstrate low transfer efficiency of carbon inputs to aged SOC which is the meaningful carbon component for long-term SOC sequestration. Additionally, we reveal that SOC aging and carbon input transiting are two distinct processes, which should be simultaneously, but mechanistical-separately, considered to predict and manage SOC dynamics in response to carbon input changes under climate and land management changes.Soil contains a lot of carbon, and its levels can change based on climate and how we manage the land. Our global soil research shows that when new carbon goes into the soil, about 25% of it leaves within a year, regardless of depth. After 30 years, only about 13% remains. Interestingly, most of the carbon in the soil is older than 30 years, showing that it can store carbon for a long time. We found that transferring carbon inputs to aged soil organic carbon (SOC) is not very efficient. This aged SOC is crucial for long-term carbon storage, which can help combat climate change. We also discovered that SOC aging and carbon input transit are separate processes. To manage soil carbon well in response to climate and land changes, we need to consider these processes separately but at the same time. In conclusion, our research reveals how carbon behaves in soil and stresses the importance of aged SOC for long-term carbon storage. Understanding these processes better can lead to more effective strategies for managing and protecting our soils, contributing to the fight against climate change.Around 80% of carbon inputs leave soil in 10 years after entering and do not contribute to aged soil carbon component The low transfer efficiency of carbon inputs to aged soil carbon undermines the feasibility of managing carbon inputs for soil carbon sequestration The dynamics of new carbon inputs and aged soil carbon are influenced by distinct climatic and edaphic attributes