青藏高原东部高寒草甸区放牧家畜粪花粉组合特征及其环境指示意义

Characteristics and environmental implications of dung pollen assemblages of grazing livestock in alpine meadow in the eastern Qinghai-Tibetan Plateau

青藏高原是我国重要的高寒草甸分布区和畜牧区,畜牧活动对区域植被和生态的影响作用受到众多学者的广泛关注。通过采集青藏高原东部高寒草甸区共49个放牧家畜粪样品(牦牛粪样品30个、马粪样品11个、羊粪样品8个),并在区域植被调查的基础上,对粪样品开展了花粉分析。结果表明:这3种类型的粪样品花粉组合以莎草科(Cyperaceae)、禾本科(Poaceae)、龙胆科(Gentianaceae)、毛茛科(Ranunculaceae)花粉为主,可较好地反映区域植被群落特征,食草动物粪花粉中有少量谷物类禾本科花粉出现反映了当地居民少量耕种燕麦用来饲养牲畜。3种放牧家畜在采食习性上存在一定差异,牦牛采食的植物种类比羊和马略多,牦牛和马对杂草类禾本科和唐松草属植物的采食率低于羊,对龙胆科、菊科和蒿属植物的采食率明显高于羊。放牧家畜通过选择性采食适口性好的莎草科和禾本科优势植物种类直接影响高寒草甸区植被群落结构和功能。研究区粪花粉组合与表土花粉组合对比发现,乔木花粉和紫菀属花粉含量在表土样品中显著高于粪样品,而禾本科和龙胆科花粉含量在粪样品中高于表土样品,上述差异指示粪花粉更能反映区域植被群落特征,放牧家畜选择性采食导致粪花粉与表土花粉组合有所区别。本研究为评估青藏高原放牧家畜采食习性以及畜牧活动对区域植被的影响提供了新的研究思路和手段,也为今后在青藏高原开展考古遗址中保存的粪样品花粉分析,据此重建古植被群落和古人类生产活动信息,提供了重要的现代过程依据和借鉴资料。

The Qinghai-Tibetan Plateau is an important area of alpine meadow pasture and livestock husbandry in China.The impact of grazing activity on the vegetation and ecology in the Qinghai-Tibetan Plateau has attracted widespread attention from many scholars.To study the impact of grazing activity on regional vegetation,we collected 49 dung samples of grazing livestock(comprising 30 yak dung,11 horse dung,and 8 sheep dung)from the typical alpine meadow in the eastern Qinghai-Tibetan Plateau.Our study area extended from 34°30′08″−35°06′28″N,101°30′57″−101°42′04″E,with elevations ranging between 3456 m and 3815 m.The vegetation communities in the sampling sites were also investigated during the field work.Principal component analysis was used to explore the characteristics of the different dung samples and pollen taxa.Meanwhile,the pollen assemblage of the dung samples was compared with the topsoil pollen assemblages in the study area to examine the selective grazing characteristics of the different livestock in the Qinghai-Tibetan Plateau.These results indicate that the pollen assemblages in the three types of livestock’s dung samples were dominated by Cyperaceae,Poaceae,Gentianaceae,and Ranunculaceae,generally reflecting the characteristics of the regional plant communities.However,there are some differences in the feeding habits of the three kinds of grazing livestock:the feeding rates of yaks and horses to Poaceae and Thalictrum species are lower than those of sheep,and those to Gentianaceae,Compositae,and Artemisia species are significantly higher than those of sheep.In addition,cereal Poaceae pollen appeared in the dung samples,reflecting the behavior of the local residents in cultivating oats to raise their livestock.Grazing livestock directly affects the vegetation community structure of alpine meadow through selective feeding of the dominant plant species of Cyperaceae and Poaceae.The comparison of the pollen assemblages of the dung and topsoil samples in the study area indicates that the contents of Cyperaceae,Polygonaceae,Ranunculaceae,Taraxacum,and Artemisia were similar.However,the contents of Poaceae and Gentianaceae in the dung samples were higher than those in the topsoil samples,and the content of Aster in the topsoil samples was higher than that in dung samples,suggesting the selective feeding characteristics of the grazing livestock.Additionally,the content of arboreal pollen,including Betula,Pinus,Picea,and Hippophae,in the topsoil samples was higher than those in the dung samples,indicating that the dung pollen assemblages could better reflect the characteristics of the local vegetation community.This study provides a new research approach for assessing the grazing habits of livestock and impact of grazing activity on regional vegetation in the Qinghai-Tibetan Plateau.Additionally,the study of pollen assemblages in modern dung samples provides an important reference for the fossil dung pollen assemblages in the archaeological sites to infer the past vegetation and ancient humans’subsistence strategy on the Qinghai-Tibetan Plateau.