Pollen-vegetation relationship and pollen preservation on the Northeastern Qinghai-Tibetan Plateau.

摘要

Qinghai-Tibetan Plateau is one of the most sensitive areas to climate change of the earth, owing to its unique topographic features and ecosystem. Soil pollen analysis is an important component of palaeo-ecological research, while pollen preservation and the relationship between pollen and vegetation can influence the correct interpretation of fossil pollen spectra. In this paper, 36 pollen samples, which come from four meadows and two forest soil pollen profiles, have been analysed to determine relationships between pollen and vegetation and pollen preservation on the northeastern Qinghai-Tibetan Plateau. The relationship between pollen and vegetation shows that the surface pollen assemblages can represent regional vegetation characteristics moderately, while Betula and Populus pollen is absent in the soil surface for Betula and Populus mixed forest. Artemisia, Chenopodiaceae, Ephedra, Pinus, Hippophae etc. are over-represented pollen taxa, Leguminosae, Ranunculaceae, Rosaceae, Gramineae etc. are under-represented pollen taxa. The study of pollen preservation indicates that pollen concentrations decrease with the increase of soil depths, more pollen taxa are present in surface soils than in deep levels, and more than 75% pollen grains will be lost from the surface soils to deep levels. Pollen sorting preservation function should be noticed. Artemisia and Chenopodiaceae can be preserved well and have higher pollen percentages in deeper levels. Cyperaceae and Populus are preserved worse, Populus pollen is absent and Cyperaceae has higher pollen percentages in the surface soil than in the deep levels. The high soil pH values are the most destructive factors for pollen preservation on the northeastern Qinghai-Tibetan Plateau. Pollen concentrations decrease sharply when the soil pH values are over 7.6. Downward leaching of pollen is unimportant in this study..