Native soil organic-carbon contents shape distinct bacterial communities associated with priming effect

Terrestrial carbon (C) cycling is mostly determined by its primed C, which is influenced by the amount and quality of soil organic matter (SOM) and by the addition of exogenous organic C. Changes in the soil microbiome to the mineralization of native soil organic C (SOC) by the priming effect in response to different amounts of SOM, however, are not fully known. We examined priming effect and microbial biodiversity in Mollisols with low (Low-SOC), medium (Medium-SOC), and high (High-SOC) SOC contents, with or without the addition of 13 C-glucose and 13 C-alanine, on day 3 of a 60-day incubation experiment when priming effect and CO 2 production were the most intense in our previous study. The soils differed in the extent to which exogenous organic C stimulated priming and the microbiome. CO 2 -C produced from native soil was 216 and 80% higher in the High-SOC than the Medium- and Low-SOC soils, respectively. The input of exogenous organic C induced a positive priming effect, which was highest in the High-SOC soil (average of 37.4 μg g -1 ), followed by the Medium- (19.6 μg g -1 ) and Low-SOC (9.0 μg g -1 ) soils. Structural equation modeling indicated that soil microbial biomass C and dissolved organic C had positive impacts on substrate-induced priming effects, mainly and indirectly driven by the effects on bacterial biomass and diversity. The various SOC soils affected the distinct key taxa within the bacterial networks, with Streptomyces and Haliangium as the key taxa least affected by changes in soils differing in SOC content. These findings are crucial for microbial strategies that drive priming effect for optimizing practices of agricultural management and understanding soil C cycles and environmental conditions. • The substrate-induced PE of native SOC varied in soils differing in SOC content. • The amounts of DOC and MBC were the main factors affecting PE. • Reduced mineralization of substrate-C with increasing bacterial diversity stimulated C retention.