Study area
The present study was undertaken at the Lanzhou University Research Station in Maqu County, Gansu Province, China (101°53′E, 33°58′N, 3500 m a.s.l.). This area is located in the northeast of the QTP. The climate is cold and humid, with only a warm season (May to September) and cold season (October to April) (Sun et al. 2015). There is no absolute frost-free period throughout the year. The annual average temperature is about 1.2 °C, and the highest temperatures are from June to August, with an average of <12 °C; the lowest temperatures (average of −10 °C) are from December to February. The average annual rainfall is ~620 mm, which occurs mainly during the forage growing season (May to September). These soils are classified as Mat-Cryic Cambisols based on previous experimental work (Sun et al. 2015), and the vegetation is characteristic of a typical alpine meadow (Yang et al. 2019). Cyperaceae (Kobresia graminifolia , Kobresia humilis , and Kobresia pygmaea ) constitute the constructive species, and Gramineae (Elymus nutans and Poa pratensis ), Compositae (Saussurea hieracioides , Aster diplostephioides , and Anaphalis lacteal ), Ranunculaceae (Saussurea hieracioides , Anaphalis lacteal , Anemone rivularis , Anemone trullifolia , and Anemone obtusiloba ), and other associated plants are widely distributed among them, in addition to scattered Potentilla fruticosa shrubs (Yang et al. 2019). The entire study area has undulating mountains, with steep and changeable, complex, and fragmented terrain.