Search

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]

From 2004 to 2010, the Sino-German research group MAGIM (Matter fluxes of Grasslands in Inner Mongolia as affected by grazing) ran a grazing experiment in a typical steppe ecosystem in Inner Mongolia, North China. Multiple ecological effects of grazing, climate variability and topography on plant and animal productivity, plant species composition change, decomposition and mineralization, soil nitrogen and organic matter distributions and dynamics, soil physics and chemistry, and soil-atmosphere gas exchange were measured in fenced plots with defined stocking rates and under different grazing management systems. This paper reviews and synthesizes the most important outcomes, conclusions, and open questions from the different project groups, as published in 125 ISI articles. While greenhouse gas fluxes, plant properties, and livestock performance were particularly responsive to (inter-) annual climate variability, soil properties were more affected by grazing intensity. Various management options based on the project results for semi-arid grasslands under changing climatic conditions are discussed. [ABSTRACT FROM AUTHOR]