MATERIALS AND METHODS
Experimental sites
The study area is located in the lower reaches of the Heihe
River, extending between latitudes 4020′–4230′N and
longitudes 9930′–10200′E, in the county of Ejina, Inner
Mongolia, Northwest China, with an area of 3104 km2
(Li et al., 2001). This region has a continental climate with
a mean annual temperature of approximately 8 C, a
maximum daily temperature of 41 C (July) and a
minimum of 36 C