Abstract
Grazing by large ungulates had both acceleration and deceleration effects on primary productivity and nutrient cycling in grassland ecosystems. The directions of these effects can differ among ecosystems because climate is one of the most important determinant. In Mongolian steppe, the ecosystem type is changed with latitudinal gradient of the aridity from forest-steppe in the north to steppe in the middle to gobi-steppe in the south. Our objective was to clarify the effects of livestock grazing on the surface soil chemical properties in three types of Mongolian steppe ecosystems along an aridity gradient. The soil samples (0.10 cm) were taken from inside and outside of the exclosure fence to analyze soil chemical properties and to determine net nitrogen (N) transformation rates for laboratory incubation. The elements essentially for the plants were decreased and net N transformations were decelerated along aridity with increasing soil pH. The effects of grazing were not prominent for the soil nutrient pools. However, the grazing decelerated net N transformation rates, especially drier incubation condition, and increased soil pH. These results suggested that grazing by large ungulates decelerated nutrient cycling, which might caused by increased alkalinity in Mongolian steppe ecosystems.
