Soil Enzyme Activities and Nematode Communities Vary with Distance from a Road in a Western Sichuan Alpine Meadow

Alpine meadows in western Sichuan form a key ecological barrier along the eastern margin of the Qinghai–Tibetan Plateau, yet belowground ecological variation associated with roads remains poorly resolved. Here, we examined soil physicochemical properties, enzyme activities and nematode communities in an alpine meadow on Zheduo Mountain along a road-distance gradient at 6, 12 and 18 m from an unpaved tourist road. Bulk soil physicochemical properties did not differ significantly among distance classes, whereas α-glucosidase, urease and catalase activities showed significant spatial variation (p < 0.05), suggesting that enzymatic processes may be more responsive than relatively stable soil nutrient pools. Total nematode abundance remained unchanged, but community composition, trophic structure and life-history composition showed directional variation across the gradient. Bacterial feeders dominated all distance classes (53–59%), and c-p 4 taxa accounted for 44–59% of the community. Low-c-p taxa were relatively more abundant at 6 m, whereas high-c-p taxa were most abundant at 18 m. Among diversity and ecological indices, only the abundance-based coverage estimator (ACE) and evenness index J differed significantly, both at 12 m. Energy-flux allocation and most functional indices showed only non-significant directional patterns. Exploratory redundancy analysis identified urease as the strongest marginal correlate of nematode-community variation, explaining 53.3% of the variation when fitted alone (p = 0.004), whereas amylase accounted for an additional 17.8% of variation in the forward-selection model (conditional p = 0.022). Together, these results reveal a contrast between relatively stable bulk soil properties and more responsive biochemical and selected nematode-community attributes along the road-distance gradient. Given the limited sample size and lack of independent road-level replication, these patterns should be regarded as exploratory evidence of spatial ecological differentiation rather than causal effects of road disturbance.