Global Biogeography of Fungal and Bacterial Biomass Carbon in Topsoil

We synthesized 1323 combinations of phospholipid fatty acid-derived fungal biomass C (FBC), bacterial biomass C (BBC), and fungi:bacteria (F:B) ratio in topsoil, spanning 11 major biomes. We found that the FBC, BBC, and F:B ratio display clear biogeographic patterns along latitude and environmental gradients including mean annual temperature, mean annual precipitation, net primary productivity, root C density, soil temperature, soil moisture, and edaphic properties. At the biome level, the highest FBC and BBC densities are observed in tundra, at 3684 (95% confidence interval: 1678~8084) mg kg-1 and 428 (237~774) mg kg-1, respectively. The lowest FBC and BBC densities were found in deserts, at 16.92 (14.4~19.89) mg kg-1 and 6.83 (6.1~7.65) mg kg-1, respectively. While the F:B ratio ranges from 1.8 (1.6~2.1) in savanna to 8.6 (6.7~11.0) in tundra. Combining an empirical model of F:B ratio with the global dataset of soil microbial biomass C, we then produced global maps for FBC and BBC in 0-30 cm topsoil. Global stock of C was estimated to be 12.6 (6.6~16.4) Pg C in FBC and 4.3 (0.5~10.3) Pg C in BBC in topsoil. This work creates a benchmark for explicit use of microbial data in modelling biosphere-atmosphere feedbacks in a changing environment.