Warming alters fresh-carbon assimilating bacterial community relevant to priming effect in Mollisols

Soil microbial response to warming may potentially contribute to the positive priming effect, i.e., accelerating the decomposition of native soil organic carbon (SOC) under the outsourced carbon (C) input. Investigating microbiota that metabolize the outsourced C is essential to deciphering the mechanism of priming effect in response to warming and thus mitigating the SOC loss under warming climate. In this work, we monitored the priming effect at 25℃, 35℃ and 45℃ over four weeks with weekly addition of ¹³C-glucose, and subsequently revealed microbial assemblage metabolizing glucose with the DNA stable-isotope probing (DNA-SIP) method. Warming initially inhibited the priming effect, and decreased bacterial α-diversity, K/r-strategists ratio (K/r) and recalcitrant C/labile C gene ratio (R/L) in week 1, suggesting that at the onset of the outsourced C input, the increased proportion of r-strategists preferentially utilize the added glucose over SOC to meet their C and energy demands. Yet, in week 4, positive priming effects were intensified by warming with up to 3.8-fold increase at 45℃. Additionally, the primed C was positively correlated with K/r, R/L, and the abundances of chitin degradation genes in week 4. These functions concurred with an increase in the abundance of resource-acquisition strategists such as Streptomyces affiliated to Actinobacteria under warming conditions over time. From week 1 to 4, warming induced a distinctive change in glucose-assimilating bacterial community compositions with a particular decrease in the relative abundance of Actinobacteria while an enriched abundance of Chloroflexi. Taken together, warming-triggered change of priming effect depended on alternation of microbiota and metabolic function over time. These findings provide important insights of how warming mediates microbial metabolic use of fresh C and subsequent SOC mineralization, reflecting the positive feedback between soil C emission and climate warming.