Study On Relative Source Area Of Pollen And Relative Pollen Productivity Of The Barkol Desert Steppe In Xinjiang

The reconstruction of land cover changes in the geological historical period is the key to understand the regular of past climate change and to predict and evaluate the effect of future global warming.Vegetation is the main manifestation of land cover,and the study of its change process and succession history has become a hot spot in academic circles.Currently,pollen is the most widely used ancient vegetation substitute index due to its small size,wide distribution,and easy preservation.However,due to factors such as pollen productivity,transportation process,and pollen preservation,there is not a simple linear relationship between pollen and vegetation.Therefore,research on relative source area of pollen and relative pollen productivity has become an important research direction of current palynology.Desert steppe is the most fragile area on the earth's land surface with simple species composition and low vegetation coverage.It is an ideal area for relative source area of pollen and relative pollen productivity estimation.Based on the analysis of modern surface soil pollen and detailed vegetation survey of 36 samples in the desert steppe area of barkol basin,Xinjiang,this paper calculates the pollen deposition rate of Tamariaceae,Artemisia,Chenopodiaceae,Compositae,Poaceace and Ephedraceae in the study area.Then,we use the ERV model to estimate their relative pollen productivity and relative source area of pollen.Finally,we use the landscape reconstruction algorithm to test the reliability of relative pollen productivity of the above plants.The research results are as follows:The surface vegetation in the Barkol desert steppe is dominated by herbs and shrubs,without tree types,most of them are Chenopodiaceae,Poaceace and Artemisia.The vegetation coverage is low.What's more,pollen assemblage is also dominated by herbs and shrubs.Due to the influence of nearby mountainous areas,tree vegetation components appear in the pollen samples.Based on the long and short axis length of the ellipsoidal pollen and the particle size of the spherical pollen,calculating pollen fall speed of Tamariaceae(0.012 m/s),Artemisia(0.012m/s),Chenopodiaceae(0.014 m/s),Compositae(0.014 m/s),Poaceace(0.028 m/s)and Ephedraceae(0.053 m/s).Among them,except for Ephedraceae,which is heavy pollen,others are light pollen.In this study,the Prentice vegetation distance weighting method is combined with ERV sub-model 2 to estimate relative source area of pollen of 255 meters in Barkol desert steppe area.Relative pollen productivity of Tamariaceae(1.50±0.13),Artemisia(16.15±1.41),Chenopodiaceae(28.39±1.62),Ephedraceae(22.87±0.76)and Compositae(20.50±2.68)are obtained by using Poaceace as the reference species(RPP=1).In addition,the landscape reconstruction algorithm is used to test the estimated relative pollen productivity of 6 taxa.Except for Tamarixaceae,which is overestimated,the difference between simulated vegetation abundance and actual vegetation abundance of other taxa are small,and the relative pollen productivity is reliable,which can be applied to vegetation reconstruction.