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Soil labile organic carbon (C) oxidation drives the flux of carbon dioxide (CO) between soils and the atmosphere. However, the impact of grazing management and the contribution soil aggregate size classes (ASCs) to labile organic C from grassland soils is unclear. We evaluated the effects of grazing intensity and soil ASC on the soil labile organic C, including CO production, microbial biomass C, and dissolved organic C and nitrogen (N) mineralization in topsoils (0-10 cm) in Inner Mongolia, Northern China. Soil samples were separated into ASCs of 0-630 μm [fine ASC (fASC)], 630-2000 μm [medium ASC (mASC)] and >2000 μm [coarse ASC (cASC)]. The results showed that heavy grazing (HG) and continuous grazing (CG) increased soil labile organic C significantly compared to an ungrazed site since 1999 (UG99) and an ungrazed site since 1979 (UG79). For winter grazing site (WG), no significant differences were found. CO production was highest in cASC, while lowest in fASC. Microbial biomass C and dissolved organic C showed the highest values in mASC and were significantly lower in fASC. Grazing increased N mineralization in bulk soils, while it exhibited complex effects in the three ASCs. The results suggest that the rate of C mineralization was related to the rate of N accumulation. To reduce CO emission and nutrient loss, and to improve soil quality and productivity, a grazing system with moderate intensity is suggested. [ABSTRACT FROM AUTHOR]

Analysis of the spatial variability of soil properties is important to interpret the site-specific ecosystems not only with respect to process investigations but also to model upscaling. This paper aims to study the effects of the grazing intensity on soil physical and mechanical properties and their interactions in a Leymus chinensis steppe of the Xilin River Basin, Inner Mongolia, China. The investigated sites were subjected to five grazing intensities (ungrazed since 1979, ungrazed since 1999, winter grazing, continuous grazing and heavy grazing). Soil water content (SWC), hydraulic conductivity (K), water drop penetration time (WDPT), shear strength (SS), soil organic carbon (SOC) concentration, bulk density (BD), and soil texture were measured at a grid with 15m sampling distance on the surface soil during the period of 2004–2005. The data were analyzed using descriptive statistics and geostatistics. The correlation and interaction between soil properties were analyzed by the methods of Pearson correlation, partial correlation and multiple regression analysis. The results showed that spatial distributions of soil properties could be well described by spherical or exponential models. The ranges of spatial dependence were the highest for WDPT and the lowest for SS. Grazing decreased SWC, SOC and WDPT but increased BD and SS. Multiple regression analysis showed significant correlations among SWC, K, WDPT, SOC and BD; as well as between SS and silt content. Soil compaction induced by sheep trampling, especially in the heavily grazed site, inclined to a homogenous spatial distribution of soil properties, which will possibly enhance soil vulnerability to water and nutrient loss, and consequently reduce the plant available water and thus grassland productivity. [Copyright &y& Elsevier]