*2.1. Study Area*

This study investigated shrublands on the northeastern Tibetan Plateau (Figure 1). Shrublands are one of the most widely distributed ecosystems on the plateau [23]. Shrublands compose woody vegetation, with coverage of more than 30% and a mean height below5m[24] and are primarily classified as desert shrublands or alpine shrublands [23]. Desert shrublands are mostly distributed in drier areas, such as the Qaidam Basin, and are characterized by species that can endure severe drought, such as *Kalidium foliatum* (Pall.) Moq, *Salsola abrotanoides* Bunge, and *Sympegma regelii* Bunge. Compared with alpine shrublands, only a few types of super-xerophytic herbs grow in desert shrublands. Brown desert soil and grey brown desert soil are mainly soil types in desert shrublands ecosystems, while soil in desert shrublands is very thin and more infertile than that in alpine shrublands [23]. In contrast, alpine shrublands are located in mountains with a cold and semiarid environment. Chestnut soil, grey cinnamon soil, and alpine shrubby meadow soil are mainly soil types in alpine shrublands ecosystems [23]. Representative species include *Rhododendron thymifolium* Maxim, *R. capitatum* Maxim, and *Sibiraea laevigata* (Linn.) Maxim. Mesophyte herbs, including *Kobresia* spp., *Carex* spp., and

*Oxytropis* spp., are located in alpine desertblands. MAP and MAT in the study regions range from 17.6 to 764.4 mm and −5.6 to 8.9 ◦C, respectively [25].

**Figure 1.** Distribution of 65 sampling sites in the shrublands of the Tibetan Plateau, which was based on the vegetation of China (1:100 0000) [26].

### *2.2. Field Investigation and Laboratory Measurements*

In line with China's vegetation atlas (1:1000000) [26] and field investigations, we systematically selected 195 plots in 65 sites across the northeastern Tibetan Plateau shrublands in July and August from 2011 to 2013 (Figure 1). We selected three plots (1 m × 1 m) at each site and the distance of two plots was between 5 m and 50 m. At each site, all of the litter, including older litter and decomposed litter in the three plots, was collected to determine the litter standing crop [27]. Also, all shrubland plants in three plots were harvested to measure aboveground biomass. The samples of litter and aboveground biomass were oven dried at 65 ◦C to a constant weight, and weighed to the nearest 0.01 g. The litters were primarily foliage or branches. Carbon content of litter was determined using an elemental analyzer (2400 II CHNS; Perkin-Elmer, Boston, MA, USA).
