Fig. 2

The relationship between soil soluble Na content and Soil electrical conductivity (EC) at different depth: a 0–20 cm; b 20–40 cm; c 40–60 cm. d The soil soluble Na content at different depths. Different uppercase and lowercase letters indicate significant differences (p < 0.05) at different soil depth in habitats (SH) and gravel desert habitats (GDH), respectively; the P-value above the bars indicates the difference between SH and GDH at the same soil depth. The correlations were evaluated by using standardized major axis regression