The long-distance transport of toxic elements is a crucial external source of metals accumulated in remote forest ecosystems. Due to the harsh environmental conditions and the complexity and diversity of influencing factors in remote alpine ecosystems, research on toxic elements is very limited, especially in the dry zone. In this regard, mercury (Hg) and arsenic (As) in soil and plant samples were investigated in a Qinghai spruce forest ecosystem at Sidalong Forest Farm (SDL), in the Qilian Mountains, northwest China. The results of the study showed a significant variation in the spatial distribution of Hg and As in soils, but a highly similar spatial distribution trend was found in mosses. High Hg and As concentrations in plants were found in moss, bark, and litterfall; the concentration of Hg was particularly high (BCF > 1). The Qilian Mountain spruce forest ecosystem was contaminated with exogenous Hg and As, with Hg, in particular, being the most serious form of contamination. The study results can provide baseline data for future forest management and research in the spruce forest ecosystem in Qinghai, northwest China.

Forest litter is an important guarantee for maintaining forest soil fertility and circulating material in forest ecosystems. The input of litter plays an important role in soil organic matter formation and biogeochemical cycles in forest ecosystems. However, the production and elements concentrations of Juniperus przewalskii (JP) litter in the Qilian Mountains are still unknown. In this study, we investigated the production of needle, branch and bark, cone, and impurity litters. We determined the concentrations and fluxes of major (K, Mg, Al, and Fe) and trace (Na, Mn, Zn, Cr, Ni, Cu, Pb, Co, Cd, and Ag) elements in needle litter of JP from September 2020 to August 2021. The results showed that the annual litter production was 4040.74 ± 495.96 kg ha⁻¹ a⁻¹. Needle and cone litters were the main components of the total litter production. The major elements (MEs) and trace elements (TEs) fluxes of litter were consistent with the litter production trend. The concentrations and fluxes of MEs and TEs in needle litter decreased in the order: K > Mg > Al > Fe > Na > Mn > Zn > Cr > Ni > Cu > Pb > Co > Cd > Ag. These results have important implications for understanding the migration processes of MEs and TEs in forest ecosystems of the Qilian Mountains.