Allocation of mass and stability of soil aggregate in different types of Nei Mongol grasslands

Aims Soil aggregate is an important component of soil structure, playing an important role in the physical and biological protection mechanism of soil organic carbon (SOC) through isolating SOC from microorganisms. As far as we know, there are few studies, however, on exploring the spatial distribution of soil aggregate at the regional scale. Our objective was to investigate the mass allocation and stability of soil aggregate in different types of Nei Mongol grasslands. Methods We have established 78 sites with a size of 10 m × 10 m across the transect of Nei Mongol grasslands and collected soil samples from different soil depth up to 1 m. We used wet sieving method to separate different sizes of aggregate partition and used mean mass diameter (MMD) and geometric mean diameter (GMD) in order to evaluate the stability of soil aggregate. The two-way ANOVA was used to test the difference of mass percentage and stability of soil aggregate in different grassland types and soil depths. In addition, a linear regression analysis was used to analyze the correlations of mass percentage and stability of soil aggregate with both mean annual precipitation (MAP) and mean annual temperature (MAT). Important findings The results showed that the mass percentages of soil aggregate were highest in meadow steppe, while almost equal in typical steppe and desert steppe. However, no significant patterns were found along the soil depth. The mass percentage of soil aggregate fractions were positively correlated with MAP in all soil layers, but negatively correlated with MAT except the layer of 70-100 cm. For the stability of soil aggregate, at 0-10 and 10-20 cm, MMD and GMD of meadow steppe were significantly greater than those of typical and desert steppes, whereas no significant differences among three grassland types were found for other soil layers. Besides, MMD and GMD in meadow steppe and typical steppe gradually decreased along the soil depth.