Microbial functional genes driving the positive priming effect in forest soils along an elevation gradient

The priming effect is a pivotal mechanism for microbial regulation of soil C cycling; however, the microbial mechanisms underlying priming effects remain elusive. Here, we combined an isotopic approach with metagenomic sequencing to investigate priming effects at five forest sites along an elevational gradient. Positive priming effects were found across the Quercus aliena var. acutiserrata (low elevation), Q. wutaishanica (low-mid elevation), Betula albosinensis (mid elevation), Abies fargesii Franch (mid-high elevation), and Larix chinensis Beissn (high elevation) forest sites. A significant positive correlation was found between the abundance of microbial C decomposition genes and priming effects (p < 0.05). Further analysis revealed that the microbial functional genes for breaking down stable C (lignin, lipids, and chitin) predominately drove the positive priming effects. Moreover, we found strong correlations between the relative abundance of eight near-complete bacterial genome bins and the priming effect. Five out of the eight genomes were associated with the Proteobacteria, indicating their predominant role in priming effects. Our results revealed that SOM quality (soil organic C, total nitrogen, and ratio of alkyl-C to O-alkyl-C), and soil environment (pH and bulk density) were the major drivers of the priming effect in forest soils as they regulated the abundance of microbial decomposition genes. In conclusion, the present study investigated the metagenomic basis of the priming effect, highlighting the importance of bacteria in association with substrate and environmental factors for C decomposition in forest soils.