The soil microbiome drives priming effects in forests at a continental scale

Abstract

The priming effect (PE), the changes in the mineralization of native soil organic carbon (SOC) in response to fresh C inputs, is a crucial biogeochemical process that affects soil C dynamics. However, how soil microorganisms regulate priming effects (positive or negative PE) at a continental scale is still unclear, potentially hampering us to better understand forest C-climate change feedback. To address this knowledge gap, we explored the controlling factors of the variation in soil PE from tropical to cold temperate forests using high-throughput sequencing and 13C-glucose tracers. Our results showed that sites with the positive PE (64.3%) were more than those with the negative ones in China’s forest. The soil microbiome (i.e., abundance of bacterial and fungal taxa) explained the largest portion of variation in priming effects (31%) compared to climate, plant traits, mineral protection, and substrate quantity properties. Specifically, abundance of bacterial taxa had a negative correlation with PE, while fungal taxa showed a positive one. Basidiomycota is the most important microbial phylum in regulating positive and negative PE, accounting for 26% of fungal taxa for positive PE and 10% for negative PE. Our results provide robust evidence that keystone taxa play a pivotal role in regulating apparent priming effects, with important implications for accurately predicting C cycling under global change.