Effect of Gap Position on the Heavy Metal Contents of Epiphytic Mosses and Lichens on the Fallen Logs and Standing Trees in an Alpine Forest

To understand the role of the forest gaps and epiphytic mosses and lichens in the heavy metal cycles of forest ecosystems, the biomass, concentration, and storage of Cd, Pb, Cu, and Zn in epiphytic mosses and lichens on fallen logs and standing trees from the gap center to the closed canopy of an alpine forest ecosystem on the eastern Tibetan Plateau were investigated. Mosses were the dominant epiphytes on fallen logs and standing trees and contribute 82.1–95.1% of total epiphyte biomass in the alpine forest. A significantly higher biomass of epiphytic mosses and lichens was observed at the gap edge. The heavy metals concentration in mosses and lichens on fallen logs and standing trees varied widely with gap positions. Lower concentrations of Cd, Cu, and Pb were found in the mosses and lichens under the closed canopy, higher concentrations of Cd and Pb were detected in the mosses and lichens at the gap edge, and higher concentrations of Cu were found at the gap center. A significant difference in Zn concentration was observed between the mosses and lichens. No significant differences in Pb or Zn concentrations were observed in the mosses and lichens between the fallen log and standing tree substrates. Furthermore, the epiphytic mosses and lichens at the gap edge accumulated more Cd, Pb, and Cu, whereas the epiphytic lichens on the fallen logs and large shrubs at the gap center accumulated more Zn. In conclusion, gap regeneration accelerates the cycling of heavy metals in alpine forest ecosystems by promoting the growth of epiphytic mosses and lichens on fallen logs and standing trees at gap edges and increasing the concentration of heavy metals in these plants. View Full-Text