Abstract Soil organic matter (SOM) dynamics plays a crucial role in soil ecosystem functioning and global warming. SOM is normally degraded slowly, but its decomposition rate can change substantially after addition of easily decomposable C sources. This process, known as “the priming effect”, has already been described in 1926 but is still poorly understood. Priming can be positive (extra decomposition of SOM) or negative (reduction of SOM decomposition), depending on the amount and physicochemical characteristics of added compounds, the composition of SOM and the metabolic abilities of responding microorganisms. We propose that the understanding of priming effects can be greatly advanced by investigating the level of convergence between the chemical characteristics of the added compound and SOM fractions, and the functional potential of microbial communities. This can be achieved by combining two different disciplines-microbial ecology and biogeochemistry. Such knowledge will deliver information under which conditions sequestration of soil carbon can be expected and provide possibilities to steer soil carbon dynamics in sustainable agricultural systems.