Heavy metal concentrations in timberline trees of eastern Tibetan Plateau

Concentrations of 14 heavy metals (Ag, As, Cd, Co, Cr, Cu, Hg, Mo, Ni, Pb, Sb, Tl, V, and Zn) in needles, twigs, bark and xylem of spruce and fir collected at the timberline of eight sites along the Hengduan Mountains, eastern Tibetan Plateau, are reported. Twigs had the highest concentration for most of elements, while xylem had the lowest concentration. The connections between elements in twigs were much richer than other organ/tissues. Pb, Ni, As, Sb, Co, Cd, Hg, Cr and Tl which are partly through anthropogenic sources and brought in by monsoon, have been accumulated in twigs and needles by wet or dry deposition in south and east sites where are within or near pollutant sources. Under moderate pollution situation, vegetation are able to adjust the nutrient element (Cu and Zn) cycle rate, thus maintain a stable concentration level. Seldom V, Ag, and Mo are from external anthropogenic sources. Needles and twigs can be used as biomonitors for ecosystem environment when needles can simply distinguish the origin of elements and twigs are more sensitive to extra heavy metal input.