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

Abstract

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 ∼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.