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 HR and GL (Table 2). The soil bulk density of the CK plot in the 20-40 cm layer was the smallest, but the difference has not reached a significant level. Moreover, the contents of total N and total P in the XS 0-20 cm layer were significantly higher than those in the other three vegetation types (P < 0.05). The maximum total N content of the soil in the 20-40 cm layer appeared in the HR plot, and the maximum total P content appeared in the GL plot, but the difference in vegetation type to soil total N and total P content did not reach a significant level. 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 N and total P 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 (Fig. 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 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 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).