A biophysical tipping point in soil texture guides the sustainable design of utility-scale solar parks.

Utility-scale photovoltaic (PV) development can generate ecological co-benefits in drylands, but whether these benefits persist across engineered microhabitats and soil backgrounds remains unresolved. This study examined 109 plots in the Talatan alpine dryland solar park to distinguish local configuration effects from texture-dependent heterogeneity in soil-quality responses. An optimized and interpretable Soil Quality Index (SQIOPT) was derived using CatBoost, while regression, SHAP, and Causal Forest analyses were used to quantify local microhabitat effects, identify the dominant global predictors of SQIOPT, and evaluate variation in PV-associated effects along the soil-fines gradient. The fixed-panel shaded (FS) microhabitat was the only PV microhabitat showing a significant decline in SQIOPT relative to reference grassland (-0.061, p = 0.043), whereas the other PV microhabitats showed no significant differences. Fixed-panel shading therefore represented the clearest local configuration-specific pressure, whereas silt and clay emerged as the dominant global predictors of SQIOPT. The estimated PV-associated effect declined with increasing soil fines and revealed a regional biophysical tipping point near 33.5%, marking a shift in soil-quality responses from positive buffering to negative constraint. The bootstrap interval of 18.4-36.8% delineated the surrounding regional sensitivity zone, and 20.2% of the sampled PV plots occurred above the tipping point. These findings show that engineering configuration organizes where local ecological pressure is expressed, whereas soil texture regulates how that pressure is translated into soil-quality outcomes. This framework recasts PV ecological co-benefits as conditional on infrastructure-soil matching and provides a basis for incorporating soil functional suitability into dryland solar planning.