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The construction of highways in the subalpine mountains generates many cut slopes. Currently, the restoration of cut slope mainly focuses on the aboveground landscapes and slope stability. Yet, it remains elusive about the belowground ecosystem functions at the early stage of restoration. In this study, we evaluated the belowground ecosystem functions of cut slopes that had been restored approximately 3 years using soil enzymatic activities, microbial biomass, and stoichiometry as the proxies. The results indicated that the phenol oxidase activity was higher in cut slopes, while the activities of β-1,4-glucosidase, β-1,4-N-acetylglucosaminidase, leucine aminopeptidase, and acid phosphatase were lower in cut slope soils compared with natural soils. Soil nitrogen availabilities (total and/or ammonium nitrogen) showed high negative correlations with the phenol oxidase activity and positive correlations with the activities of almost all other enzymes. These results suggested that soil nitrogen was the key factor in driving the shifts of enzymatic activities across two types of soils. Moreover, we found the imbalance of soil nutrients in cut slope soils, especially the carbon vs. nitrogen and the nitrogen vs. phosphorus. By applying the vector analysis, we found that the vector A values were more than 45° in all samples, suggesting that microbial phosphorus limitation occurred in both cut slope and natural soils. These findings suggested that maintaining the balance of soil nutrient supplies is important to the recovery of the below-ground ecosystem functions at the early restoration stage of cut slopes. This study provided new insights into designing the ecological restoration strategies for cut slopes by considering the belowground ecosystem functions.

Roadway rock-cut slopes have a strong effect on soil organic carbon (SOC), its fractions and overall soil health. However, it is still unknown how SOC fraction properties are influenced under different aspect conditions. We quantified differences in artificial SOC fractions, soil nutrients, and enzyme activities across eight types of roadway rock-cut slopes in Songpan, China. On slopes in landslide areas, four aspects (S, W, N, E) were selected for study, and four equivalent aspects on slopes not affected by a landslide were selected as a reference. SOC, easily oxidizable organic carbon (EOC), particulate organic carbon (POC), urease, sucrase, total nitrogen (TN), and carbon pool management index (CPMI) significantly differed among non-landslide aspects, however, except for POC and urease, did not differ with aspect on landslide-affected slopes. In contrast, dissolved organic carbon (DOC), nitrate nitrogen (NO3–-N), and ammonia nitrogen (NH4+-N) significantly differed among aspects on landslide-affected slopes, while they did not significantly differ on aspects of non-landslide slopes. However, higher SOC, EOC, POC, TN, urease, sucrase, and CPMI occurred on non-landslide slopes than landslide-affected slopes of the same aspect, suggesting that landslide slopes may face serious degradation. Our findings indicate that slope aspect and the occurrence of landslides have an influence on SOC pools, and consequently on CPMI.