| Summary: | The priming effect (PE) is important for understanding the decomposition of soil organic matter (SOM) and forecasting C-climate feedback. However, there are limited studies on microbial community-level properties and the keystone taxa involved in the process. In this study, we collected soil from a subtropical <i>Phyllostachys edulis</i> forest undergoing long-term N-addition and conducted an incubation experiment to evaluate the effects of single and repeated addition of <sup>13</sup>C-labeled glucose. Our results demonstrated that previously N-fertilized soil had a smaller cumulative PE compared with that of the control (11% average decrease). This could be primarily explained (26%) by the lower abundance of bacterial r-strategy group members (B_mod#2, constituting Proteobacteria, Firmicutes, and Actinobacteria phyla) under N-addition treatments. A single C-addition induced a greater PE than that of repeated C-additions (2.66- to 3.11-fold). Single C addition led to greater C to N ratios of microbial biomass and fungi to bacteria, positively impacting cumulative PE, indicating that the shifts in fungal/bacterial dominance play an important role in regulating PE. Moreover, a saprophytic taxa group (F_Mod#3, primarily composed of the phyla Ascomycota) explained 62% of the differences in cumulative PE between single and repeated C-additions. Compared with repeated C-additions, a greater abundance of B_Mod#2 and F_Mod#3, as well as C-related hydrolase activity, was observed under single C-addition, inducing greater cumulative PE. Therefore, sufficient C may facilitate the proliferation of r-strategy bacterial taxa and saprophytic fungal taxa, thereby increasing SOM decomposition. Our findings provide novel insights into the relationship between microbial community-level properties and PE.
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