3.1. Variation of soil physical and chemical properties in different vegetation types
The type of vegetation had significant effects on the soil’s basic physical and chemical properties. The bulk density of the 0-20 cm CK soil layer was significantly lower than both in both HR and GL (Table 2).
The contents of total nitrogen and total phosphorus in the XS 0-20 cm layer were significantly higher than those in the other three vegetation types (P < 0.05). The soil bulk density of the 20-40 cm layer under all four vegetation types was higher than that in the 0-20 cm layer, while the total porosity, total nitrogen and total phosphorus in the 20-40 cm soil layer were lower than in the 0-20 cm layer.
3.2. Variation of soil carbon fractions in different vegetation types
There were significant differences in EOC, POC, and SOC under the four types of vegetation (Figure 2).
There were no significant differences in the soil MBC content among the four types of vegetation in the 0-20 cm layer. The MBC content in the 20-40 cm layer of HR vegetation was significantly higher than in the other three vegetation types. Except for the MBC contents of the HR vegetation, the MBC, EOC, POC, and SOC contents in other vegetation types decreased significantly as soil depth increased. At the 0-20 cm layer, the EOC contents of the GL vegetation was 1.44, 2.82, and 2.06 g/kg higher than XS, HR, and CK, respectively, while at the 20-40 cm layer the EOC contents was 0.63, 1.01, and 0.95 g/kg higher than XS, HR, and CK, respectively. The POC and SOC contents in the 0-20 cm layer of XS vegetation were significantly higher than those in the other three vegetation types. The soil POC content in HR vegetation and the SOC content in GL vegetation at the 20-40 cm layer were the highest. The maximum values of soil POC and SOC were 0.37 and 1.61 g/kg higher than the minimum values, respectively. A two-way ANOVA analysis demonstrated significant associations between soil depth and vegetation type on organic carbon components (MBC, EOC, POC and SOC) in all the samples measured (Table 3).