| Summary: | Biochar induces various priming effects on native soil organic carbon (nSOC), whereas the underlying mechanisms linking these to soil microbial community structure and functions remain unclear. To investigate soil microbial community structure and functions associated with priming effects, rice straw (RS) and the derived biochar samples (RS400 and RS700, pyrolyzed at 400 °C and 700 °C, respectively) were applied to a sandy loam soil for a 33- and 200-day incubation. Using stable C isotopic ratios, CO2-C emissions from biochar/feedstock and nSOC were quantitatively identified and indicated an enhanced C stability of RS700 over that of RS and RS400. A decreased soil pH and increased dissolved organic carbon and NH4+-N concentrations with the RS amendment are driving forces that lead to an enhanced soil microbial activity and a higher abundance of heterotrophic microbes, especially Proteobacteria and Acidobacteria, which contribute to high CO2 emissions. The enhanced C stability of biochar and nSOC over that of pristine feedstock was primarily attributable to a stable and high soil pH, which minimized the disturbance of soil heterotrophic microbial community structure and functions, favoring the growth of Actinobacteria, Proteobacteria, and Ascomycota. The biochar amendment in soil enriched the metabolic pathways of biosynthesis and the decomposition of secondary metabolites, polycyclic aromatic hydrocarbons (PAHs) degradation, and electron transfer carriers. Keywords: Biochar stability, Priming effect, Microbial community structure, Metabolic function, Stable C isotope
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