Abstract. Surface soils interact strongly with both climate and
biota and provide fundamental ecosystem services that maintain food,
climate and human security. However, the quantitative linkages between soil
properties, climate and biota remain unclear at the global scale. By
compiling a comprehensive global soil database, we mapped eight major soil
properties (bulk density; clay, silt, and sand fractions; soil pH; soil
organic carbon, SOC, density; soil total nitrogen, STN, density; and soil
C:N mass ratios) in the surface soil layer (0–30 cm), based on machine
learning algorithms, and demonstrated the quantitative linkages between
surface soil properties, climate and biota at the global scale, which we
call the global soil–climate–biome diagram. In the diagram, bulk density
increased significantly with higher mean annual temperature (MAT) and lower
mean annual precipitation (MAP); soil clay fraction increased significantly
with higher MAT and MAP; soil pH decreased with higher MAP and lower MAT
and the “critical MAP”, which means the corresponding MAP at a soil pH of =7.0 (a shift from alkaline to acidic soil), decreased with lower MAT. SOC
density and STN density were both jointly affected by MAT and MAP, showing
an increase at lower MAT and a saturation towards higher MAP. Surface soil
physical and chemical properties also showed remarkable variation across
biomes. The soil–climate–biome diagram suggests shifts in soil
properties under global climate and land cover change.