Characteristics Of Modern Pollen-Fungal Spore Assemblage And Its Paleo-Environmental Implications In The Northeastern Tibetan Plateau

The Qinghai-Tibetan Plateau(QTP)is sensitive to global climate change because of its unique natural geographical unit,which is an important ecological security barrier for China and even Asia.Pollen and fungal spores are effective proxies,which played an important role in the study of palaeoclimate,vegetation evolution and human activities.The northeastern QTP is the typical agro-pastoral ecotone in China,and it is also an important corridor for prehistoric people to enter the hinterland of the plateau.The coupling process and mechanism between past environmental change,ecological succession and human activities has become a fucos of research on the QTP,and the pollen and fungal spores are useful methods to study these issues.In this study,we have collected 84 topsoil samples from 5 vegetation units,49 dung samples from domestic herbivores and 28 fossil samples from the Gaqing section.The results indicated that pollen assemblages could resonablly reflect the regional vegetation communitis,as well as domesticated herbivores feeding habits;fungal spore assembalges are vary in different vegetation communites,and some spore-types are coprophilous and sensitive to regional grazing intensity.TCCF is an ideal proxy to reconstruct the variations of grazing intensity on the QTP.Here are the conclusions:(1)The pollen assemblage in the topsoil samples of the five vegetation communities in the northeastern of QTP was dominated by herbaceous and shrub pollens,accounting for more than 90% of the total,and the topsoil pollens could represent the regional vegetation conmmunities.The pollen-types of Rosaceae,Compositae,Fabaceae and Ranunculaceae show high percentages in the sampling sites from the heavy grazed alpine meadow community.Poaceae and Brassicaceae pollens are significant indicators for agricultural activities on the plateau.The pollen assemblages in the three types of livestock's dung samples are dominated by Cyperaceae,Poaceae,Gentianaceae and Ranunculaceae,which can generally reflect the characteristics of regional plant communities.However,there are some differences in the feeding habits of the three kinds of grazing livestock,The contents of Poaceae and Thalictrum pollen are lower in yak and horse dung samples than that in sheep dung,while Gentianaceae,Compositae and Artemisia pollen are significantly higher than that in sheep dung.Additionally,Cereal-Poaceae pollen appeared in the dung samples,which reflect the behaviour of local residents cultivated oat to raise the livestock.(2)The fungal spores in the feces of domesic herbivores are domimated by Sporormiella spp.,Urocystis sp.,Sordaria spp.,Pleospora spp.,Glomus spp.and QTPF-01.In topsoil samples,Savoryella spp.is the most dominant species in the cropland samples,while Meliola spp.and Coniochaeta spp.,are closely related to alpine forest environments.The fungal spore assemblage of alpine shrub,alpine meadow and alpine steppe are characterized by Glomus spp.,Savoryella spp.,Valsaria spp.,Enorrhiza spp.and QTPF-03.Comparison of fungal spore assemblages between herbivore dung and topsoil showed that Sporormiella spp.,Urocystis sp.,Sordaria spp.,Pleospora spp.,QTPF-01,Podospora spp.,Delitschia A.and QTPF-07 are the most reliable fecal indicators.The total concentrations of coprophilous fungal spores is sensitive to grazing pressure and could be used to reconstruct the grazing intensity on the QTP.(3)Fossil pollen and fungal spores records from the Gaqing section indicated that the vegetation types in the northeastern QTP are Cyperaceae dominatd alpine meadows developed since early Holocene,and the climate is relatively cool and humid.In the middle Holocene(4.3-8.2 cal ka BP),Picea pollen increased significantly,which may be related to the expansion of spruce forest in the mountain valleys of northeastern QTP.Human related pollen(Compositae and Chenopodiaceae)and the concetrations of coprophilous fungal spores(Sporormiella spp.,Urocystis sp.,Sordaria spp.,Podospora spp.,Delitschia spp.)increased since about 4.3 ka.These evidences indicate that the livestock economy dominated the production pattern in the northeastern part of the QTP during the middle Holocene.Therefore,the present study on the characteristics of modern pollen-fungal spore assemblages will provide more accurate modern process basis and reference data for the reconstruction of paleo-vegetation communities and prehistoric human activities since the Holocene.