Global patterns and drivers of soil microbial biomass C, N, and P 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 C (SMB C), N (SMB N),
and P (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 3,801 observations for SMB C, 3,154 observations
of SMB N, and 2,429 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. In general, the global mean values of SMB
C, N, and P concentrations were 693.0 mg kg-1, 89.5 mg kg-1, and 35.5 mg
kg-1, respectively. These mean values belie a significantly spatial
heterogeneity of these concentrations across biomes and a clear
latitudinal trend (wherein SMB C, N, and P increase in cold and high
latitude environments along with the large soil organic carbon, SOC). SOC
was the most important factor regulating SMB C, N, and P at a global
scale. At the global scale, the storage of SMB C, N, and P was 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.