Negative priming effect on mineralization in a soil free of vegetation for 80 years

The priming effect (PE) is a complex process corresponding to a modification of mineralization rates of soil organic matter (SOM) following inputs of fresh organic matter (FOM). The priming effect can be either positive or negative (i.e. an acceleration or retardation of SOM decomposition) and is controlled by several factors such as microbial community composition, SOM chemical structure and nutrient availability. The first objective of our experiment was to study negative or positive PE of stabilized SOM. The second was to identify the role of FOM decomposers in the PE of stabilized SOM. We incubated, for 39 days, a fallow soil free of vegetation for 80 years amended with C-13-cellulose and inoculated with a FOM-decomposing community. The soil contained stabilized SOM. The PE of the stable organic matter was always negative and tended to be more negative when the FOM-decomposing community was added. This suggests that for this particular soil, SOM mineralization was not limited by energy. Moreover, as the inoculation of a FOM-decomposing community led to a more negative PE, we assume that the FOM-decomposing community facilitated the access of FOM to the indigenous bare soil community.