This study was carried out on Qilianshan Mountain, located
in the upper Heihe River Basin, in pure stands of P. crassifolia
located on a bench within a north-facing slope at 2800 m elevation
in the Pailougou watershed (100◦17
E, 38◦24
N) (Fig. 1),
50 km south of Zhangye, Gansu province, during the 2011 growing
season. From 1994 to 2010, the mean annual air temperature
was 0.5 ◦C, the mean maximum and minimum temperatures was
28.0 ◦C and −36.0 ◦C, respectively. Annual precipitation is between
290.2 mm and 467.8 mm, with rainfall occurring mainly from June
to September (60.0% of the annual total). The pan evaporation was
1051.7 mm.