Sensitivity and regulation factors of soil organic carbon content in steppe and desert—steppe grasslands of the Mongolian Plateau

Soil organic carbon (SOC) content dominates the organic carbon pools in grasslands. Thus, factors that influence and regulate SOC content must be clarified when addressing global climate change. We investigated SOC in the top 10 cm of the soil layer from 109 plots of the Mongolian Plateau, including both desert-steppe and steppe landscapes. We then examined the association between SOC with grazing intensity, climatic factors, soil properties, and vegetation diversity indices. Desert-steppe samples had lower mean SOC than steppe samples (0.3% versus 1.5%). Desert-steppe SOC did not vary with grazing intensity, but steppe SOC did. Instead, desert-steppe SOC decreased and increased, respectively, with higher growing season temperature and soil electrical conductivity; these two variables were the major factors influencing SOC in this grassland type. Besides grazing, outside growing season precipitation and soil pH were the major environmental factors that correlated positively with steppe SOC. The SOC of steppe grasslands was more sensitive to grazing than SOC of desert-steppe grasslands. Additionally, while climate, grazing, soil, and vegetation all regulated SOC, the most influential variables differed between the two grassland types. These findings enhance our understanding of SOC regulatory mechanisms in different grasslands on the Mongolian Plateau. Such knowledge is crucial for predicting the consequences of environmental change on carbon sequestration.