Carbon sequestration in the subsoil and the time required to stabilize carbon for climate change mitigation

• Published in: Global change biology Vol. 30; no. 1; pp. e17153 - n/a
• Main Authors: Sierra, Carlos A., Ahrens, Bernhard, Bolinder, Martin A., Braakhekke, Maarten C., Fromm, Sophie, Kätterer, Thomas, Luo, Zhongkui, Parvin, Nargish, Wang, Guocheng
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01.01.2024
• Subjects: Advection; Biological activity; Bioturbation; Carbon; Carbon 14; Carbon capture and storage; Carbon sequestration; Climate change; Climate change mitigation; Climate Research; diffusion–advection–reaction; Klimatforskning; Liquid phases; Markvetenskap; Mathematical models; Microbial activity; microbial decomposition; Microorganisms; organic matter stabilization; radiocarbon; Radiocarbon dating; Soil; soil carbon sequestration; Soil formation; Soil Science; Soils; Subsoils; Transit time; Vertical profiles; diffusion-advection-reaction; climate change mitigation; microbial decomposition; organic matter stabilization; transit time; radiocarbon; soil carbon sequestration
• ISSN: 1354-1013; 1365-2486; 1365-2486
• DOI: 10.1111/gcb.17153

Soils store large quantities of carbon in the subsoil (below 0.2 m depth) that is generally old and believed to be stabilized over centuries to millennia, which suggests that subsoil carbon sequestration (CS) can be used as a strategy for climate change mitigation. In this article, we review the main biophysical processes that contribute to carbon storage in subsoil and the main mathematical models used to represent these processes. Our guiding objective is to review whether a process understanding of soil carbon movement in the vertical profile can help us to assess carbon storage and persistence at timescales relevant for climate change mitigation. Bioturbation, liquid phase transport, belowground carbon inputs, mineral association, and microbial activity are the main processes contributing to the formation of soil carbon profiles, and these processes are represented in models using the diffusion–advection–reaction paradigm. Based on simulation examples and measurements from carbon and radiocarbon profiles across biomes, we found that advective and diffusive transport may only play a secondary role in the formation of soil carbon profiles. The difference between vertical root inputs and decomposition seems to play a primary role in determining the shape of carbon change with depth. Using the transit time of carbon to assess the timescales of carbon storage of new inputs, we show that only small quantities of new carbon inputs travel through the profile and can be stabilized for time horizons longer than 50 years, implying that activities that promote CS in the subsoil must take into consideration the very small quantities that can be stabilized in the long term. We reviewed mathematical models that represent soil carbon dynamics with depth and found thatmost models adopt the diffusion, advection, reaction (decomposition) paradigm. Transport processes play a secondary role in shaping soil carbon profiles, with the difference betweencarbon inputs and decomposition (g) playing a major role. Carbon stocks in the subsoil can be increased by decreasing the rate of change of soil carbon withdepth, increasing vertical transport (v) or decreasing g.