Climate controls the global distribution of soil organic and inorganic carbon

Abstract

Soil organic carbon (SOC) and inorganic carbon (SIC) are key components of soil carbon, each playing a distinct role in soil health, carbon cycling, and climate regulation. However, their relative distributions across the global lands remains understudied. Here through analysing two data-driven global estimates of SOC and SIC, we found distinct distributions of SIC and SOC along vertical soil depths, among different land covers, soil orders and climate zones. While the density of SOC is higher in top soils, there are more SIC in deep soils. Vegetation shifts the relative distribution of SIC vs. SOC, with the ratio between SIC and SOC (${\log }_{10}\frac{\mathrm{SIC}}{\mathrm{SOC}}$) decreasing progressively from bare soils, cropland, grassland to forest. Climate plays a major role in shaping ${\log }_{10}\frac{\mathrm{SIC}}{\mathrm{SOC}}$, accounting for 66 % of variations in top soil (0–0.3 m), 65 % in mid soil (0.3–1 m), and 74 % in deep soil (1–2 m). Higher temperature favours the preservation of SIC compared to SOC, as revealed by the positive relationship between ${\log }_{10}\frac{\mathrm{SIC}}{\mathrm{SOC}}$ and MAT. The close link between key climate variables and the distribution of SIC vs. SOC indicates that future climate change is highly likely to alter the composition of soil carbon. Our finding provides support for differentiated soil carbon preservation strategies under different environment.