Global links between soil microbes and biogeochemical functions

Soil contains immense stocks of carbon, which may accelerate climate change if released. Soil microbes affect these carbon stocks by producing decomposition-catalyzing enzymes, a capacity varying across different microbial groups. Consequently, establishing links between global variation in microbial communities and functions should substantially enhance future projections of soil carbon. To this end, we here reveal global patterns in soil microbial community function using nearly 13,000 observations of microbial biomass, community structure, and enzyme activities (>100,000 measurements). We find total biomass and fungal and Gram-negative bacterial dominance increase with latitude, whereas Gram-positive bacteria predominate near the equator. Enzyme stoichiometry correspondingly suggests greater nitrogen and carbon limitation at higher latitudes. Comparing microbial and enzyme patterns, fungal biomass indicates nitrogen limitation, whereas Gram-negative bacterial biomass indicates carbon limitation. Together, microbial community structure explains significant variation in enzyme profile uncaptured by climate, soil properties, or landcover. Soil microbial communities dominated by fungi and Gram-negative bacteria exhibit less enzyme activity per unit biomass, with two- to four-fold variation in temperature- and biomass-normalized activity rate observed across the Earth. Significant functional differences thus arise with global turnover in microbial communities, indicating that community structure merits a central position in process-based soil models.