Influence of grazing on soil water and gas fluxes of two Inner Mongolian steppe ecosystems

Intensive overgrazing, practiced for the last decades in Inner Mongolia, has led to serious grassland degradation and deterioration of soil structure. As a consequence, the soil gas and water fluxes and therefore soil functions were affected by grazing. We investigated two steppe ecosystems characterized by two plant communities: Stipa grandis (SG) and Leymus chinensis (LCh) and different grazing intensities: ungrazed since 1979 (UG79), continuously grazed (CG, at the SG site) and winter grazed (WG, at the LCh site). The undisturbed soil samples, for determination of saturated (ks) and unsaturated (ku) hydraulic conductivities and air conductivities (ka), were collected in vertical and horizontal direction from two soil horizons. The coefficients of anisotropy were calculated as ratios of the values obtained for the samples taken in horizontal direction to the values of the vertical samples. The results indicated a good recovery of soil structure at the sites ungrazed for more than 30 years. Furthermore, the recovery was more pronounced at the LCh site compared with the SG site. The results suggested that grazing causes significant changes in anisotropy of soil functions related to rearrangement of aggregates and creation of a platy soil structure. The results of the coefficients of anisotropy of hydraulic conductivity showed that they depend on the matric potential for both treatments.