Spatial variation of roadside soil quality and its key influencing factors on the Qinghai-Xizang Plateau.

Investigation on the soil quality and its influencing factors along the highways of the Qinghai-Xizang Plateau holds significant value for understanding the ecological environment of high-altitude regions. Principal component analysis was utilized to identify the minimum dataset and establish a soil quality index evaluation system based on physicochemical property indicators of surface soil samples collected from road-side locations in representative areas of the Plateau. By integrating spatial zoning and altitude gradient analysis, this study reveals the spatial variations in soil quality both horizontally and vertically. The results show that the final minimum dataset comprised soil organic matter, total phosphorus, C/N ratio, and N/P ratio, which effectively reflected regional soil quality variances; soil organic matter carried the highest weight and acted as the primary evaluation indicator. Clear spatial disparities in soil quality were evident: values were relatively elevated in the eastern and southern plateau but lower in western and northern regions. Along altitudinal gradients, soil quality reached its peak at middle elevations (3200-4500 m) and decreased at low (2700-3100 m) and high elevations (4500-5100 m). Precipitation, temperature, and vegetation types along altitudinal gradients mainly governed soil quality variability by controlling litter input, microbial decomposition, and soil organic matter accumulation, with soil organic matter playing a crucial role as a key mediator linking environmental gradients to soil quality shifts. The proposed SQI-MDS framework effectively characterizes soil quality variations with fewer indicators and reduced survey costs, offering scientific support for large-scale soil resource monitoring and ecological environment management on the Qinghai-Xizang Plateau.