Airborne Pollen Assemblages And Their Relationships With Climate In The Central And Eastern Typical Area Of The Loess Plateau

As the basis of interpretation the fossil pollen spectrum correctly and accurately, thestudy of modern pollen process is very necessary. The research of airborne pollen is one ofimportant contents of modern pollen process, and is also play an important role in the researchof pollen dispersal, source area and the relationship with vegetation and climate. LuochuanCounty and Hunyuan County are the typical areas of the Loess Plateau. Through the analysisand contrast of the airborne pollen assemblages and fluxes in different areas, different yearsand different seasons, this paper try to reveal the characters of airborne pollen in differentregions of the loess plateau, through the correlation analysis between pollen and the climateparameters in different seasons, to discuss the main controlled factors to the pollen quantity indifferent seasons and in different areas.The general characteristics of the airborne pollen assemblages in these two regions from2007to2009indicate that herbs dominate the airborne pollen assemblages with similar thefluxes, while the pollen fluxes of trees and shrubs are significant higher in Luochuan regionthan in Hunyuan, that is closely correlated with the vegetation composition: Luochuan islocated in the transition zone of forest and steppe, whereas Hunyuan belongs to steppe,suggesting that the pollen assemblages could generally reflect the regional vegetationcharacters. The pollen assemblages in Luochuan County show that Quercus, Pinus and Ulmusown the highest percentages successively in the trees pollen assemblages; Rosaceae,Elaeagnaceae and Ostryopsis have the highest proportion in shrubs successively; Artemisia,Chenopodiaceae and Poaceae dominate herbaceous pollen assemblages successively. Themain pollen types in Hunyuan area are consistent with that in Luochuan, but the order ofpercentages is different for each taxa. In Hunyuan, Ulmus owns the highest contents in thetrees pollen assemblages, then Pinus and Quercus; Ostryopsis has the highest percentages inthe shrubs pollen assemblages and then Elaeagnaceae and Rosaceae.In Luochuan area, the tree pollen percentages are higher than30%in2007-2008,indicating the characteristics of forest vegetation wih precipitation higher than500mm, whilethe tree pollen percentages are less than10%and the herbaceous pollen percentages arehigher than80%in2008-2009,indicating the characteristics of grassland vegetation withprecipitation less than450mm. That maybe suggesting that change of pollen assemblages canreflect the climate change more sensitively than the vegetation in Luochuan.The comparison of airborne pollen proportions in different seasons shows that both ofthe areas, trees and shrubs have higher pollen proportions in spring than in other seasons, especially in April and May; Herbs have high pollen proportions in all the seasons, especiallyin summer, autumn and winter, its pollen proportions can reach to more than90%, suggestingthat the pollen assemblages in loess plateau have some common regional characteristics.The comparison of airborne pollen fluxes in different seasons shows that from2007to2009, the pollen highest fluxes values appear in the late summer season, the second highestvalue appear in spring in Luochuan, while the total pollen fluxes and tree fluxes are lower inthe spring of2008-2009than in the spring of2007-2008and herbaceous pollen fluxes arehigher especially for Artemisia in the summer and autumn of2008-2009than in the summerand autumn2007-2008; In Hunyuan, the overall character of pollen assemblages are similarwith Luochuan, but the pollen fluxes peak appear in the spring in2007-2008, while appear inthe late summer to early autumn in2008-2009.The correlation analysis between climate parameter and airborne pollen fluxes showedthat woody pollen taxa have more significant correlations with climate than herbaceous pollentaxa; and temperature and humidity have a obvious influence on pollen fluxeses in LuochuanCounty than that in Hunyuan County, while the wind speed has more significant influence onpollen fluxes in Hunyuan County than that in Luochuan County. However, the same pollentaxon is controlled by different climate factors in different areas and in different seasons. Theresult in Luochuan County indicates that: in spring, the woody pollen fluxes increase with theincrease of temperature,; Apart from spring, Pinus and Rosaceae pollen fluxes reduce with theincrease of humidity; Pollen fluxes of Ulmus (in winter), Quercus and Rosaceae (in thesummer and autumn) increase with the increase of temperature, and Rosaceae also havesignificant positive correlation with wind speed in winter. Most of the herbaceous pollenfluxes are mainly affected by the relative humidity and wind speed in spring and winter, thelower relative humidity and the higher wind speed are benefit to the increase of herbaceouspollen fluxes. In addition, Chenopodiaceae, Poaceae and Cereals were also affected by thespring temperature, and the pollen fluxes rise with the increase of temperature. Compositaefluxes were also affected by temperature, humidity and wind speed in summer and autumn,when the lower temperature and humidity, and higher wind speed are benefit to the increaseof pollen fluxes. Compared with Luochuan County, wind speed will influence pollen fluxesfor most taxa in all the seasons in Hunyuan County, pollen fluxes increase with the increaseof wind speed; moreover, most of the woody pollen fluxes, just as in Luochuan, are alsoinfluenced by temperature, and the higher temperature will benefit to the increase of pollenfluxes; in addition, the low relative humidity in the summer and autumn will benefit to theincrease of the pollen fluxes; Besides, Ulmus (in the summer, autumn and winter) and Rosaceae(in the summer and autumn) have a certain positive correlation to the averagetemperature, and Pinus have negative correlations with the relative humidity. In addition,most herbaceous pollen fluxes also have some negative correlation with relative humidity inwinter.