Microbial Functional Genes Help Explain Soil Carbon Sensitivity to Temperature Across Global Biomes.

The temperature sensitivity of soil microbial respiration (Q10) is a major factor underpinning global soil carbon emissions under climate change. While microbial biomass is a key driver of Q10 values, the role of microbial functional traits in explaining Q10 values remains largely undetermined. Here, we combined temperature-gradient incubations with a metagenomic database generated from a collection of surface soils collected across 196 natural ecosystems spanning all major biomes. We found that microbial functional traits related to carbohydrate metabolism and hemicellulose degradation, quantified as transcripts-per-million (TPM), are significantly correlated with Q10 values. Moreover, Q10 values display abrupt non-linear shifts once thresholds of microbial functional traits are crossed. Global mapping further provides evidence that microbial functional traits associated with carbon degradation and high Q10 values are concentrated within the planet's largest soil carbon reservoirs at high latitudes in the Northern Hemisphere. These regions could represent critical hotspots of vulnerability to soil carbon losses under climate warming. Our results provide a new step towards incorporating metagenomic data and non-linear microbial responses into next-generation carbon-climate models.