The biogeography of soil fungal and bacterial biomass is tied to the efficiency of decomposition at global scale

Variation in relative abundance of bacteria and fungi within the soil microbiome could drive striking differences in carbon uptake and release across different biomes. However, a lack of global information on the relative abundance of these organisms in terrestrial ecosystems has prevented the inclusion of soil bacterial and fungal biomass and associate processes into global biogeochemical models. Here, we use >3000 distinct observations of soil fungal and bacterial abundance to explore the environmental drivers of variation in fungal: bacterial dominance and to generate the first quantitative and spatially explicit model of soil fungal proportion, defined as fungi/(fungi + bacteria), across terrestrial ecosystems. We reveal striking latitudinal trends: fungal dominance increases in cold and high latitude environments with large soil carbon stocks. The global pattern in soil fungal proportion is strongly linked to the carbon use efficiency (CUE) of soil carbon decomposition, with higher CUE in bacterial dominated soils.