The priming effect dynamics are driven by microbial activation and growth and constrained by the relative availability of input C and soil N

Fresh organic inputs can prime the decomposition of native soil organic matter (SOM) and the release of soil mineral N, yet it remains unclear whether and how soil mineral N change affects the priming effect (PE). To explain the PE dynamics, we estimated the fate of added glucose and the changes in soil mineral N, biomass and necromass of fungi and bacteria, and enzyme activities in the soils with and without addition. The PE rates peaked within day 1, decreased until day 20, and remained positive to the end of incubation on day 48 in all soils. The PE rates depended on the glucose amount after its peaks only. After the PE peaks, glucose addition increased glucose-utilizing bacterial biomass and decreased soil mineral N content on all sampling days. Glucose addition also decreased SOM-utilizing fungal biomass during the incubation in low-N soils, bacterial and fungal necromass after day 20, and enzyme activities after day 1. The PE intensity before its peak was correlated with the percentage of fungal biomass in total microbes and the ratio between soil mineral N and input C before incubation. The PE intensity after its peak depended on the amount of un-utilized glucose and mineralized soil N, and the increases in glucose-utilizing microbial biomass. These findings provided evidence for the triggering effect, re-utilization of bacterial residues by fungi, and enzyme decomposition in controlling the dynamics of a positive PE and the preferential substrate utilization for a negative PE. The physical protection of added glucose and soil N mineralization affected the PE dynamics via mediating the growth and turnover of active microbial groups utilizing added substrate and SOM.