Dual Role of Microorganisms in Soil Organic Matter Dynamics

Soil microbes function as both decomposers and synthesizers of soil organic matter.

The Science

The concept of a soil “microbial carbon pump” is proposed as a mechanism for integrating how the contrasting breakdown and synthesis activities of microorganisms—coupled with the “entombment” of microbial residues via organo-mineral interactions—influence soil organic matter (SOM) dynamics and persistence.

The Impact

A conceptual framework was developed to inspire new research aimed at the role of microorganisms in the formation of persistent SOM. New understanding on this topic is essential for model development and for informing national and global discussions on the sustainability and vulnerability of soils, including related impacts on food and biofuel production, ecosystem services, environmental health, and climate.


The dynamic balance between inputs of organic materials versus losses (via decomposition or transport) regulates SOM cycling. In this context, microbes are widely investigated as major mediators of decomposition, particularly through the effects of their extracellular enzymes. Less studied is the impact of microbial growth and death on the creation of SOM. Because the living biomass of microbes in soil is small, microbial contributions to SOM formation have been underappreciated. But, the rapid life cycle of microbes can produce large amounts of organic residues over time. Even though microbial residues can be intrinsically easy to decompose, recent studies suggest a significant portion can be stabilized in soils by intimate physical and chemical associations with soil minerals. In this perspective article, the contrasting metabolic roles that microbes play in SOM dynamics (i.e., catabolic breakdown and anabolic formation) are reviewed. The concept of a soil “microbial carbon pump” is borrowed from marine literature and coupled with the “entombing effect” (stabilization via organo-mineral interactions) to create a framework for stimulating and guiding new research efforts targeted at the role of microbial synthesis and turnover in the formation of persistent SOM.

Principal Investigator(s)

Julie Jastrow
Argonne National Laboratory

Chao Liang
Chinese Academy of Sciences


This work was supported by the Strategic Priority Research Program of the Chinese Academy of Sciences, the National Natural Science Foundation of China, the National Key Research and Development Program of China, and the Office of Biological and Environmental Research within the U.S. Department of Energy Office of Science.


Liang, C., J.P. Schimel, & J.D. Jastrow, “The importance of anabolism in microbial control over soil carbon storage.” Nature Microbiology 2(8), 17105 (2017). DOI:10.1038/nmicrobiol.2017.105