Study site
The study site was located at Haibei National Field Research Station of
the Alpine Grassland Ecosystem (37°36′ N, 101°19′ E, 3215 m a.s.l.) in
the northeastern part of the Tibetan Plateau, China. The mean annual air
temperature and precipitation were -1.2 °C and 489.0 mm during
1980-2014, respectively (Liu et al. 2018). Approximately 80% of the
precipitation was concentrated in the growing season (from May to
September). This mesic alpine grassland is dominated by Stipa
aliena , Elymus nutans and Helictotrichon tibeticum . The
soil is classified as a Mollisol according to USDA Soil Taxonomy. The
average soil bulk density, organic carbon concentration and pH were 0.8
g·cm-3, 63.1 g·kg-1 and 7.8 at the
0-10 cm soil depth, respectively (Lin et al. 2016).