Distribution and Enrichment Characteristics of Heavy Metals in Soil and Plants Along an Altitude Gradient in the Northern and Southern Mountains of Lhasa
This study investigated the altitudinal distribution and enrichment characteristics of heavy metals in the soil-plant system of the northern and southern mountains of Lhasa on the Tibetan Plateau. Soil and dominant plant samples were collected from three sites along an elevation gradient from 3,650 to 4,150 m, and concentrations of Cr, Cd, Cu, Zn, Ni, As, and Pb were analyzed. Soil heavy metal concentrations ranged from 0.06 to 184.4 mg·kg−1, with all elements except Cd and Pb exceeding local background values. Plant heavy metal concentrations were within normal ranges, indicating no obvious stress. Correlation analysis revealed significant positive correlations between soil Zn and Cd, Cr and Ni, and plant Zn and Cu. Except for Cr, Cu, and Cd, plant and soil concentrations of the same element were significantly correlated. Bioconcentration factor (BCF) analysis showed that most plants had weak enrichment capacity (BCF < 1), but five species, including Ephedra sinica and Rheum likiangense, exhibited BCF > 1 for Cd, with R. likiangense showing the highest BCF of 4.01. The enrichment capacity varied with altitude and species. Potential ecological risk assessment indicated that Cd posed a relatively high risk in plants, warranting attention. This study fills a gap in understanding the spatial distribution and enrichment of heavy metals in this region, providing a scientific basis for ecological management and environmental protection.