Soil organic carbon is the largest carbon reservoir of terrestrial ecosystems. The Microbial Carbon Pump (MCP) theory suggests that microbial necromass, or dead microbial residues, are important sources of stabilized organic carbon, but little is known about how soil food webs mediate these "microbial carbon pumps" and , in turn, affect organic carbon turnover processes.
Two research teams of the Institute of Applied Ecology (IAE) of the Chinese Academy of Sciences (CAS), the Soil Ecology Research Team and the Ecosystem Microbiology Research Team, recently conducted an indoor microcosm experiment. The leading researchers Dr. KOU Xinchang, Dr. ZHANG Xiaoke and Dr. LI Qi, together with their colleagues, used carbon-stable isotope tracing technique to study the biological transformation pathways of exogenous organic carbon and the energy flow process within the soil food web to elucidate the roles of soil food webs on soil carbon capture, or carbon sequestration.
The researchers found that soil organisms are both drivers of soil carbon cycling and sources of soil organic carbon. Approximately one third of exogenous organic carbon (straw) was transformed to dead microbial residues and became a new, stabilized component of the soil organic carbon pool. After input of the exogenous organic carbon, microbial decomposition and metabolic synthesis served as the "production pump" of the "new" carbon, the trophic cascades of soil food web served as the "driving pump" of exogenous organic carbon flow, and the accumulation of microbial residues served as the "formation pump" of the "new" carbon. The researchers further explained that the upper trophic groups of the soil food web simply acted as a "temporary storage container" of the "new" carbon. The entire process realizes the transformation of exogenous organic carbon to stable biocarbon, which is an important mechanism stabilizing soil organic carbon.
This study, funded by the National Key Research and Development Program of China, the Strategic Priority Research Program of the Chinese Academy of Sciences and the National Natural Science Foundation of China, has been published in Global Change Biology entitled "Exogenous carbon turnover within the soil food web strengthens soil carbon sequestration through microbial necromass accumulation."