Global patterns and predictors of soil microbial biomass carbon, nitrogen, and phosphorus in terrestrial ecosystems

Soil microbes play key roles in driving and regulating nutrient cycling in terrestrial ecosystems. However, a lack of global-scale information regarding the distribution of soil microbial biomass carbon (SMB C), nitrogen (SMB N), and phosphorus (SMB P) in terrestrial ecosystems has limited our ability to incorporate the broad-scale soil microbial nutritional properties and the associated processes into biogeochemical models. Here, we synthesized a global dataset including 3801 observations for SMB C, 3154 observations of SMB N, and 2429 observations of SMB P in the top 0-30 cm soil depth. Based on this comprehensive global dataset, we generated quantitative and spatially explicit maps of SMB C, N, and P across terrestrial ecosystems using a random forest approach. We also quantified the relative importance of multiple environmental variables in predicting the spatial variation of SMB C, N, and P concentrations and then made further predictions at a global scale. Soil organic carbon (SOC) was the most important factor in predicting SMB C, N, and P at a global scale. At the global scale, the storage of SMB C, N, and P were estimated to be 23.13 Pg C, 3.93 Pg N and 2.16 Pg P in the top 0-30 cm soil surface, respectively. Our global maps of SMB C, N, and P presented here can be used to constraint Earth system models, and provide the first step forward to predict the roles of soil microbial nutrients in terrestrial nutrient cycling.