Objective The aim was to investigate the soil quality condition of different stand types in Liziping Nature Reserve.

Method Four forest stand types (Cyclobalanopsis and Populus szechuanica broad-leaved mixed forest, oriental oak deciduous broad-leaved forest, Yushania lineolata forest, and fir-spruce coniferous mixed forest) in the Liziping Nature Reserve were taken as the research objects. A minimum data set (MDS) consisting of 11 indices, such as mass water content, capillary porosity, medium silt, coarse silt, clay, hydrolyzed nitrogen, organic matter, total phosphorus, total potassium, urease and microbial nitrogen, was constructed through the method of principal component analysis, so as to evaluate the soil quality condition in the region.

Result ① There was no significant difference in soil bulk density, non-capillary porosity, fine sand, total nitrogen, available potassium and microbial biomass carbon among different stand types. There were significant differences in water content, total porosity, capillary porosity, pH, clay, medium silt, coarse silt, fine sand, total potassium, microbial nitrogen, total phosphorus, available phosphorus, organic matter, hydrolyzed nitrogen, catalase, urease, acid phosphatase and urease (P < 0.05). ② There were significant positive correlations among the indices such as forest volume, forest cover, herbaceous biomass, carbon content of organs of dominant tree species, basal cover and degree of depression and the soil quality index (SQI) of the MDS in different forest stand types. Those indicated that the SQI based on the MDS can reflect the soil quality index of different forest stand types in the region, and it has good applicability. ③ The SQI of four forest stand types was distributed in the range of 0.269 ~ 0.758, the overall SQI was 0.510; the SQI of fir-spruce coniferous mixed forest was 0.758 (medium quality), Yushania lineolata forest was 0.601 (good quality), oriental oak deciduous broad-leaved forest was 0.327 (low quality), and cyclobalanopsis and populus szechuanica broad-leaved mixed forest was 0.269 (low quality). The difference of soil quality among different stand types was statistically significant (P < 0.05).

Conclusion There are significant differences (P < 0.05) in the overall SQI among different stand types, with the highest overall content of soil nutrient content and enzyme activities in the fir-spruce coniferous mixed forest. The soil quality from high to low was as follows: fir-spruce coniferous mixed forest > Yushania lineolata forest > oriental oak deciduous broad-leaved forest > cyclobalanopsis and populus szechuanica broad-leaved mixed forest. The results can provide reference for the construction of soil quality evaluation model, selection of dominant afforestation tree species and soil improvement in this area, and provide scientific decision-making basis for the protection, development and utilization of forest soil resources in local nature conservation area.