Response of plant diversity and soil nutrient condition to grazing disturbance in Stipa baicalensis Roshev. grassland.

The effect of grazing disturbance on plant diversity,soil physical and chemical properties,and soil nutrients characteristics of Stipa baicalensis Roshev.grassland was studied.The results show that the number of species,plant diversity and vegetation coverage were significantly decreased along with the increasing of grazing intensity.The effects of grazing disturbance on soil physical and chemical properties were primarily manifested in increased soil bulk density,decreased soil water content.Under heavy grazing,soil bulk density increased to 1.36 g/cm3,soil water content decreased to 12.37%,vegetation coverage reduced,and the ground biomass was also significantly lower.Grazing disturbance led to the change of soil organic carbon pattern,soil organic carbon content in 0-10 cm decreased gradually with light grazing,but the organic carbon transferring to deep soil was accelerated,organic carbon levels in 10-20 cm and 20-30 cm were significantly higher than those in other plots,and soil organic carbon content of the profile increased 7.19% than non-grazing grassland.Total soil nitrogen content(0-10 cm,10-20 cm) increased under light grazing;under medium grazing,it was significantly higher than that in other plots.Soil total phosphorus content was not significantly different among plots,except that it was decreased significantly under heavy grazing.The increase of plant diversity,aboveground biomass,and underground biomass was a response to light grazing disturbance,while under heavy grazing,plant diversity and vegetation coverage reduced,soil physical and chemical properties changed,soil nutrient resource became scarce,and grassland appeared a trend of degradation.