2.2. Experimental design and soil sampling
In the experimental site, the grassland (GL; Area: 30 m × 40 m;
35°34’54″N, 104°37’57″E) was the control group, while Xanthoceras
sorbifolia (XS; Area: 20 m × 50 m; 35°35’10″N, 104°37’7″E),Caragana korshinskii (CK; Area: 30 m × 30 m; 35°34’55″N,
104°38’1″E), and Hippophae rhamnoides (HR; Area: 20 m × 30 m;
35°34’45″N, 104°39’1″E) were designated as the three vegetation types
(Table 1). Three sample plots (with the size of 8 m × 8 m) were randomly
selected from each vegetation type for sampling.
In September 2017, the soil sampler (diameter 5 cm) was used to sample
layers (0-20, 20-40 cm) according to the diagonal 5-point method (four
points were selected at both ends of an “X”, with one point selected
at the intersection). Five soil samples of the same soil layer in each
plot were mixed to form one soil sample for a total of 24 soil samples.
After removing debris, such as stones and residual roots, the sample was
divided into two parts. One part of the fresh soil was stored in a
refrigerator at 4°C through a 2 mm soil sieve. Another part of the soil
was air-dried (direct sunlight was avoided on soil samples), placed in a
ziplock bag through a 100-mesh soil sieve, and stored in a cool and
ventilated place (storage time not exceeding one year).