Reviews and syntheses: The mechanisms underlying carbon storage in soil

Abstract

Abstract. Scientific research in the 21st century has considerably improved our knowledge of soil organic matter and its dynamics, particularly under the pressure of the global disruption of the carbon cycle. This paper reviews the processes that control C dynamics in soil, the representation of these processes over time, and their dependence on variations in major biotic and abiotic factors. The most recent advances in soil organic matter knowledge are: – Most organic matter is composed of small molecules, derived from living organisms, without transformation via additional abiotic organic polymerization. – Microbial compounds are predominant in the long term. – Primary belowground production contributes more to organic matter than aboveground inputs. – Contribution of less biodegradable compounds to soil organic matter is low in the long term. – Two major factors determine the soil organic carbon production yield from the initial substrates: the yield of carbon used by microorganisms and the association with minerals, particularly poorly crystallized minerals, which stabilize microbial compounds. – Interactions between plants and microorganisms and between microbial communities affect or even regulate carbon residence times, and therefore carbon stocks. Farming practices therefore affect soil C stocks not only through carbon inputs but also via their effect on microbial and organomineral interactions.

Microbial Necromass in Soils—Linking Microbes to Soil Processes and Carbon Turnover

“…The necromass can be decomposed by enzymes in the soil matrix that are either present as exoenzymes or released by cell autolysis (Miltner et al, 2012;Schimel and Schaeffer, 2012). In addition, mechanical disruption of the residual cell envelopes by physical processes, e.g., shrinking and swelling of SOM as well as soil mixing due to bioturbation by macrofauna may also determine the fate (Bohlen et al, 2004;Basile-Doelsch et al, 2020). The ultimate fate of the necromass then depends on many factors: microbial decay, clay content, Fe or Al oxides, water content and pore system of the soil aggregates (Schimel et al, 2007).…”

Management of Grazed Landscapes to Increase Soil Carbon Stocks in Temperate, Dryland Grasslands

“…The processes regulating carbon retention and the formation (constraint 3) and decomposition of stabilized SOM (constraint 4) depend on interactions among the composition of carbon inputs, soil texture, and microbial communities. The protection of carbon as relatively simple organic products from microbial decomposition is associated with organomineral complexes (Basile-Doelsch et al, 2020;Lavallee et al, 2020). Management can disrupt these processes, but the complexities are not well-understood (Dignac et al, 2017).…”

Accounting for soil architecture and microbial dynamics in microscale models: Current practices in soil science and the path ahead

“…As a result, the assumptions embodied in these models have become increasingly challenged in recent years. Various authors have argued that the idea of splitting SOM into distinct pools based only on chemical composition and degree of recalcitrance no longer corresponds to the latest picture available of the nature of SOM (Abramoff et al, 2018;Basile-Doelsch, Balesdent, & Pellerin, 2020;Blankinship et al, 2018;Dungait, Hopkins, Gregory, & Whitmore, 2012;Sainte-Marie et al, 2021;Yang, Zhang, Bourg, & Stone, 2021). Among the pieces of evidence that led to this perspective, Kleber et al (2011) showed that the oldest SOM contains a greater proportion of easily decomposable organic molecules, whereas the younger one contains organic structures that are supposed to be more stable, suggesting that "carbon age is not necessarily related to molecular structure or thermodynamic stability".…”