Soil microbial carbon pump: Mechanism and appraisal

The soil microbial carbon pump (MCP) conceptualizes a sequestration mechanism based on the process of microbial production of a set of new organic compounds, which carry the carbon from plant, through microbial anabolism, and enter into soil where it can be stabilized by the entombing effect. Understanding soil MCP and its related entombing effect is essential to the stewardship of ecosystem services, provided by microbial necromass in the formation and stabilization of soil organic matter as well as its resilience and vulnerability to global change. The mechanism and appraisal of soil MCP, however, remain to be elucidated. This lack of knowledge hampers the improvement of climate models and the development of land use policies. Here, I overview available knowledge to provide insights on the nature of the soil MCP in the context of two main aspects, i.e., internal features and external constraints that mechanistically influence the soil MCP operation and ultimately influence microbial necromass dynamics. The approach of biomarker amino sugars for investigation of microbial necromass and the methodological limitations are discussed. Finally, I am eager to call new investigations to obtain empirical data in soil microbial necromass research area, which urgently awaits synthesized quantitative and modeling studies to relate to soil carbon cycling and climate change.