Effect of long‐term grazing on soil organic carbon content in semiarid steppes in Inner Mongolia

Abstract To clarify the response of soil organic carbon (SOC) content to season‐long grazing in the semiarid typical steppes of Inner Mongolia, we examined the aboveground biomass and SOC in both grazing (G‐site) and no grazing (NG‐site) sites in two typical steppes dominated by Leymus chinensis and Stipa grandis , as well as one seriously degraded L. chinensis grassland dominated by Artemisia frigida . The NG‐sites had been fenced for 20 years in L. chinensis and S. grandis grasslands and for 10 years in A. frigida grassland. Aboveground biomass at G‐sites was 21–35% of that at NG‐sites in L. chinensis and S. grandis grasslands. The SOC, however, showed no significant difference between G‐site and NG‐site in both grasslands. In the NG‐sites, aboveground biomass was significantly lower in A. frigida grassland than in the other two grasslands. The SOC in A. frigida grassland was about 70% of that in L. chinensis grassland. In A. frigida grassland, aboveground biomass in the G‐site was 68–82% of that in the NG‐site, whereas SOC was significantly lower in the G‐site than in the NG‐site. Grazing elevated the surface soil pH in L. chinensis and A. frigida communities. A spatial heterogeneity in SOC and pH in the topsoil was not detected the G‐site within the minimal sampling distance of 10 m. The results suggested that compensatory growth may account for the relative stability of SOC in G‐sites in typical steppes. The SOC was sensitive to heavy grazing and difficult to recover after a significant decline caused by overgrazing in semiarid steppes.