Study On The Surface Pollen Of Gonghe Basin In Qinghai

Gonghe Basin is located between the Qilian Mountains and the Kunlun Mountains in the northeast of the Tibetan Plateau. It is in the border area of monsoon and transition zone of climate that is sensitive to changes in the environment and climate. Pollen is an important carrier of studying paleoenvironment and paleoclimate. Characteristics analysis of surface pollen provide sediment pollen assemblages an important reference and prerequisite guarantee for recovering ancient vegetation and paleoenvironment.Based on the pollen analysis of 46 surface soil samples,this article mainly summarizes the characteristics of surface pollen assemblages at the different types of vegetation communities in Gonghe Basin of Qinghai, the relationship between the distribution of typical pollens and vegetation, the analysis of pollen A/C value and pollen assemblages PC A. Preliminary draw the following conclusions:(1) The results of the surface pollen analysis show that pollen assemblage matches the corresponding plants. In the different vegetation communities. The herb and shrub pollens occupy absolute advantage of surface pollen samples, yet arbor tree pollen content is less. The percentage of herb and shrub pollens is over 79.69%in the platform steppe, desert and semi-desert, floodplain and alpine meadow communities of this study area, however the woody pollens is less than 19.76%. Which in piedmont alluvial fan, the percentage of arbor trees pollen has increased up to 37.35%, but still mainly on herbs and shrub pollen.The herb and shrub pollens are dominant by Gramineae, Cyperaceae, Ranunculaceae, Artemisia, Chenopodiaceae Nitraria, and trees pollens are mainly Pinus, Betula, Picea.(2) At the different community types of pollen assemblages,46 surface soil samples have a certain amount of tree pollen species, mainly Picea, Pinus, Betula and Populus.Refer to this study area vegetation data,it is show that there is no trees in this local.So the paper argues that the tree species pollens may be mainly from outlying areas through different propagation paths. Additional settlement point is also likely to be have affected by planted pinus pollen.(3) The distribution characteristics of typical pollens roughly correspond to the vegetation of Gonghe Basin.The percentages and absolute concentrations of herbaceous and shrub pollens can basically reflect the composition and distribution of vegetation, but the tree species pollens can not accurately reflect the presence of forest vegetation in the study area.(4) A/C values of surface pollen may reflect the overall extent of wet and dry of Gonghe Basin. In arid climate condition, Chenopodiaceae pollen holds the edge in pollen assemblages, while in semi-arid climate, Artemisia pollen has the highest percentage.Furthermore in the dry grasslands platform, artemisia pollen is not dominant.And A/C values are less than 1, even lower than the desert region, which may be subject to human activities, overgrazing and other factors that causing grassland degradation.(5) PCA analysis of surface pollen assemblages of Gonghe Basin shows that the first factor has inhibited the growth of Chenopodiaceae and Artemisia which are on behalf of the drought mainly reflecting relatively humid ecological environment; the second factor is advantageous to the growth of arid arbor trees, but go against most of herbaceous vegetation; the third factor presents the high eigenvalues of the drought-resistant Nitraria, but the eigenvalues of some representative wet pollens are low which indicates the relatively arid environment; in the fourth factor, Artemisia vegetations grow advantageously while Chenopodiaceae limited, which reflects the ambient humidity in the study area. Humidity is so impotant major factor to impact the pollen assemblages that can be used as an indicators of climate change.The ranking results of typical pollens basically correspond with the sort conditions of samples. PCA analysis can genrally distinguish the samples of different ecological environment.