MODERN POLLEN ASSEMBLAGES AND DISPERSION PROCESS IN THE QILIAN MOUNTAINS,NORTHEAST TIBETAN PLATEAU
In present paper,based on the analyses of samples from modern air pollen collectors,and pollen data from rivers(22 samples)and surface soils(430 samples)from the Qilian Mountain,the effects of wind and river on the transport of different types of pollen are discussed.The study area(35°～39°N,93°～103° E)is located on the northeastern edge of the Tibetan Plateau.Situated at the junction of the Loess Plateau,Mongolian Plateau and Tibetan Plateau,it borders the Hexi Corridor to the north and the Qaidam Basin to the south,stretching about 1000 km from east to west and 200～400 km from south to north.In this study,we focus on the differences in pollen types and percentages collected by airborne pollen collectors during the flowering phenology(woody plants:April-June;shrubs and herbs:July-September;2021～2022).The four collectors(Gulang:37.4° N,102.6°E;Minqin:39.0°N,103.6° E;Heihe upstream:40.6° N,100.0°E;and Ejina Banner:41.8° N,101.0° E)were set up on the different locations of the Shiyang and Heihe rivers.Our results show that the identified woody plant types are mainly Picea,Pinus,Cupressaceae and Betula.The main shrub types include Zygophyllaceae,Elaeagnaceae,Ephedra,Solanaceae and Fabaceae.The main herb types are Poaceae and Cyperaceae,while Artemisia and Chenopodioideae have both shrub and herb types.We assume that the pollen assemblages in airborne pollen collectors are mainly composed of near-source and regional vegetation types(＜200 km),while the proportion of long-distance transport(＞200 km)is very low.Pollen types and percentages change well with the flowering phenology.For examples,from April to June,more needle-leaved and broad-leaved pollen types are found in Gulang and Hehe River upstream areas closer to Qilian Mountains,while from July to September,Artemisia and Chenopodiaceae reached 63.9％and 62.0％,respectively.In contrast,in Minqin and Ejina Banner located in the hinterland of the basin,the proportions of woody types were very low,while more drought-adapted shrubs reached 91.0％and 93.9％from April to June,respectively.The characteristics of pollen assemblage of river sediments are closely related to the vegetation conditions surrounding the sampling sites,and there are obvious differences in pollen assemblage in terms of the flowering phenology.Thus,when using the pollen assemblages of basin sediments to reconstruct past vegetation and climate,it is necessary to fully consider the change of pollen deposition process caused by runoff and river channel changes,and further to distinguish different information of mountains and basins.Analysis of surface pollen in the Qilian Mountains region shows that samples with arboreal(conifers and broadleaves)pollen types accounting for over 40％were mainly distributed in areas above 2000 meters in elevation.As the elevation decreases to around 1200 meters,the arboreal content drops below 10％,and the changes in pollen assemblage are consistent with the current regional vegetation composition.Therefore,combining the changes in arboreal pollen content in surface soil and airborne pollen collector,it can be inferred that the changes in arboreal pollen types contained in lake sediments reflect the situation of upstream mountain arboreal pollen input into rivers and the water flow transport capacity.It should be cautious when using the relative content or ratio of Artemisia and Chenopodiaceae for vegetation or climate reconstructions in arid regions,considering these two types included many widely distributed species,and had strong pollen dispersal capabilities.Going forward we will focus on integrating the long-term airborne pollen data,exploring the characteristics of pollen assemblages on a monthly scale and their relationship with meteorological factors.This work can provide fundamental data for regional vegetation and environmental reconstructions.
万方数据
维普
