Climatic and anthropogenic controls of topsoil features in the semi-arid East Asian steppe

Topsoil characteristics and their determinants in the steppe on the central Inner Mongolian Plateau were investigated. Percentages of different grain size fractions of topsoil samples from 236 plots and corresponding standardized data of four environmental/human-activity factors, namely mean annual temperature (MAT), mean annual precipitation (MAP), human disturbance index (HDI) and land use/land cover (LULC) types were used to perform canonical correspondence analysis (CCA). The roles of both human land uses and climatic factors on topsoil grain size distribution are highlighted. Climatic factors seem to have played a significant role in determining the coarse sand (0.2-1 mm in size) percentages in the steppe and meadow by affecting the vegetation cover, while human disturbance indicated by species composition appears to have significantly influenced the percentages of clay (< 0.002 mm in size) and fine-medium silt (0.002-0.016 mm in size) in the typical steppe (P < 0.01). Soil Organic Carbon (SOC) content is negatively correlated with coarse sand percentages (P < 0.01), implying that reduction of soil fertility is linked to soil coarsening. Percentages of fine-medium silts (0.002-0.016 mm in size) are still more abundant in the area where artificial vegetation are planted and remains as the major source of dust storms. This study implies that afforestation in the steppe region has not improved soil conditions and thus reduced dust storms as earlier expected.