Younger carbon dominates global soil carbon efflux

• Published in: Global Change Biology
• Main Authors: Xiao, Liujun, Wang, Guocheng, Wang, Mingming, Zhang, Shuai, Sierra, Carlos A., Guo, Xiaowei, Chang, Jinfeng, Shi, Zhou, Luo, Zhongkui
• Other Authors: National Key Research and Development Program of China, National Natural Science Foundation of China, Postdoctoral Science Foundation of Jiangsu Province, Fundamental Research Funds for the Central Universities
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2022
• Subjects: Tundra
• Online Access: http://dx.doi.org/10.1111/gcb.16311; https://onlinelibrary.wiley.com/doi/pdf/10.1111/gcb.16311; https://onlinelibrary.wiley.com/doi/full-xml/10.1111/gcb.16311

Abstract Soil carbon (C) is comprised of a continuum of organic compounds with distinct ages (i.e., the time a C atom has experienced in soil since the C atom entered soil). The contribution of different age groups to soil C efflux is critical for understanding soil C stability and persistence, but is poorly understood due to the complexity of soil C pool age structure and potential distinct turnover behaviors of age groups. Here, we build upon the quantification of soil C transit times to infer the age of C atoms in soil C efflux ( a efflux ) from seven sequential soil layer depths down to 2 m at a global scale, and compare this age with radiocarbon‐inferred ages of C retained in corresponding soil layers ( a soil ). In the whole 0–2 m soil profile, the mean a efflux is (mean with 5%–95% quantiles) year and is just about one‐eighth of a soil ( year), demonstrating that younger C dominates soil C efflux. With increasing soil depth, both a efflux and a soil are increased, but their disparities are markedly narrowed. That is, the proportional contribution of relatively younger soil C to efflux is decreased in deeper layers, demonstrating that C inputs (new and young) stay longer in deeper layers. Across the globe, we find large spatial variability of the contribution of soil C age groups to C efflux. Especially, in deep soil layers of cold regions (e.g., boreal forests and tundra), a efflux may be older than a soil , suggesting that older C dominates C efflux only under a limited range of conditions. These results imply that most C inputs may not contribute to long‐term soil C storage, particularly in upper layers that hold the majority of new C inputs.