Fig 1.
Study area and field sampling sites.
Green indicates the distribution of the Eurasian steppe. The yellow transect is the study area, corresponding to the Eurasian steppe eastern transect (ESET) region. Black triangles represent the main cities in the study area. Gray circles indicate the field sampling sites.
Fig 2.
A structure equation model showing the hypothesized causal paths to examine the effects of climate, grazing, soil texture and vegetation on the soil organic carbon density (SOCD).
Ellipses denote the latent variables included in the model. Single-headed arrows denote the paths. Double-headed arrows indicate an interaction effect between a pair of variables.
Fig 3.
Distribution of the soil organic carbon density (SOCD) in the Inner Mongolia subregion and Mongolia grasslands subregion.
Black indicates the SOCD of the Inner Mongolia grassland subregion in different soil layers. Gray indicates the SOCD of the Mongolia grassland subregion in different soil layers. Significant differences in the SOCD between the Inner Mongolia grassland subregion and the Mongolia grassland subregion are indicated by different lowercase letters.
Table 1.
Environmental characteristics and soil organic carbon density (SOCD) in the 0–30 cm soil layer in the Eurasian steppe eastern transect (ESET) region, Inner Mongolia grassland (IMG) subregion and Mongolia grassland (MG) subregion.
Table 2.
Relationships between the soil organic carbon density (SOCD) and a series of controlling factors in three soil layers along the ESET region.
Fig 4.
Standardized total effect (direct plus indirect) of climate, soil texture, grazing and vegetation on the soil organic carbon density (SOCD).
The standardized total effect of each variable is shown separately with different colors. ESET, Eurasian steppe eastern transect; MG, Mongolia grassland; IMG, Inner Mongolia grassland.
Fig 5.
Relative importance of individual factors in controlling the soil organic carbon density in the ESET region (A), Mongolia grassland subregion (B) and Inner Mongolia grassland subregion (C). ESET, Eurasian steppe eastern transect; MG, Mongolia grassland; IMG, Inner Mongolia grassland; MAP, mean annual precipitation; MAT, mean annual temperature; GI, grazing intensity; SCC, soil clay content; PH, soil pH; BP, biomass productivity. (+) and (-) indicate positive and negative effects of the controlling factor.
Table 3.
Soil organic carbon density over 0–30 cm and mean annual precipitation (MAP) and temperature (MAT) in various grasslands.
Fig 6.
(A) Significant positive linear relationship between the mean annual temperature and mean annual precipitation along the ESET region. (B) Significant positive linear relationship between the mean annual precipitation and community biomass productivity along the ESET region. (C) Non-significant negative linear relationship between the mean annual temperature and soil clay content along the ESET region. ESET, Eurasian steppe eastern transect.