2.1 Site description
This experimental site is located in a fenced temperate steppe in Duolun County (42˚02’N, 116˚17’E, 1324 m a.s.l), Inner Mongolia, China. For the years 1960 to 2014, its mean annual temperature was 2.1°C and mean annual precipitation was 371 mm. Soil is classified as chestnut soil according to the Chinese classification, and Calcis-orthic Aridisol in the US Soil Taxonomy classification, with sand, silt, and clay contents of 62.8%, 20.3%, and 16.9%, respectively. Stipa krylovii is the most common herbaceous species in this temperate steppe; other common species include Artemisia frigida , Agropyron cristatum , Cleistogenes squarrosa , Allium bidentatum , andPotentilla acaulis (Su et al., 2018).