*2.1. Experimental Site*

This study was conducted at the Long-Term Research Station of Alpine Forest Ecosystems (31◦14 N, 102◦53 E, approximately 3600 m a.s.l.). Our experimental sites are located in an alpine forest on the eastern Tibetan Plateau [22]. The annual mean temperature and precipitation are 2.7 ◦C and 850 mm, respectively. Seasonal snow cover develops in late October and melts in the following April, with a maximum snow depth of approximately 50 cm and a soil freezing time of approximately 120 days [34]. This alpine forest is dominated by coniferous cypress (*Sabina saltuaria* (Rehder & E.H.Wilson) W.C.Cheng & W.T.Wang) and deciduous larch (*Larix mastersiana* Rehd. et Wils. ) and birch (*Betula albosinensis* Burkill). The main shrubs are dwarf willow (*Salix paraplesia* Schneid.) and azalea (*Rhododendron lapponicum* (L.) Wahl.) and there are also some sedge (*Carex* sp.) and moss at the site. Canopy opening induced by natural tree fall and other climatic extremes covers 13–23% of the landscape. Decomposition of plant detritus is limited by the low temperature; thus, soils are classified as dark brown soil. The depth of the forest floor (Oi + Oe + Oa) is 7 cm with a carbon stock of 1.6 t C ha−1. Carbon, nitrogen, phosphorus and humus contents (the sum of alkali extracted organic matter) in the organic horizon are 16, 0.58, 0.17 and 6.1%, respectively [36].
