Soil quality assessment in different climate zones of China's Wenchuan earthquake affected region

China's 2008 8.0 Ms Wenchuan earthquake and subsequent secondary geo-hazards caused widespread damage to vegetation-soil system in northwest China. In order to evaluate changes in soil quality status after damage, we established four treatments in the earthquake-affected area, including disturbed and treated sites in a dry hot climate (D-t), undisturbed sites in a dry hot climate (D-ud), disturbed and treated sites in a subtropical humid monsoon climate (S-t), and undisturbed sites in a subtropical humid monsoon climate (S-ud). Forty-eight soil samples were collected and analyzed for 27 soil physical, chemical, and biological properties. Principal components analysis (PCA) was conducted with 26 variables in significant differences except total potassium among D-t, D-ud, S-t, and S-ud. A minimum data set of soil indicators was established with available potassium (AK), K+, total salt content (TSC), and total phosphorus (TP) based on PCA results. Using the Integrated Quality Index (IQI) equation, we calculated the soil quality index (SQI). S-ud, S-t, D-ud, and D-t had mean SQI scores of 0.566, 0.275, 0.537, and 0.374, respectively. Our results showed that undisturbed sites had better soil quality compared to disturbed and treated sites based on their superior physical indicators, superior nutrient conditions, and higher microbial carbon source metabolic diversity, especially in the subtropical humid monsoon climate with frequent rainfall. The SQI reflects the variations observed in earthquake-affected area and may be considered as a suitable technique for detecting changes in soils. Our results will also supply the fundamental data for evaluating the effects, design, and implementation of restoration programs.