Distribution and Enrichment Characteristics of Heavy Metals in Soil and Plants Along an Altitude Gradient in the Northern and Southern Mountains of Lhasa

• • Soil Cr and Ni concentrations reached 1.92 and 1.70 times the local background values, respectively, indicating geogenic enrichment; Cd exceeded background at some sites, likely due to fertilizer application in afforestation projects. • • Only soil Cu and plant Cr and Ni showed significant correlations with altitude, suggesting that spatial distribution is influenced by both natural geological processes and anthropogenic activities. • • Rheum likiangense exhibited a Cd bioconcentration factor of 4.01, demonstrating typical Cd hyperaccumulator potential; its Cd enrichment increased significantly with altitude (R²=0.93, P<0.05), indicating altitude as a key controlling factor. • • Cd contributed 94.1% to the average potential ecological risk index (RI) for plants, despite the overall risk level being slight, highlighting Cd as a priority pollutant in this ecosystem.