Utility of Surface Pollen Assemblages to Delimit Eastern Eurasian Steppe Types

Modern pollen records have been used to successfully distinguish between specific prairie types in North America. Whether the pollen records can be used to detect the occurrence of Eurasian steppe, or even to further delimit various steppe types was until now unclear. Here we characterized modern pollen assemblages of meadow steppe, typical steppe and desert steppe from eastern Eurasia along an ecological humidity gradient. The multivariate ordination of the pollen data indicated that Eurasian steppe types could be clearly differentiated. The different steppe types could be distinguished primarily by xerophilous elements in the pollen assemblages. Redundancy analysis indicated that the relative abundances of Ephedra, Tamarix, Nitraria and Zygophyllaceae were positively correlated with aridity. The relative abundances of Ephedra increased from meadow steppe to typical steppe and desert steppe. Tamarix and Zygophyllaceae were found in both typical steppe and desert steppe, but not in meadow steppe. Nitraria was only found in desert steppe. The relative abundances of xerophilous elements were greater in desert steppe than in typical steppe. These findings indicate that Eurasian steppe types can be differentiated based on recent pollen rain.

现代花粉记录已被成功用于区分北美特定的草原类型。此前，学界尚未明确花粉记录能否用于检测欧亚草原（Eurasian steppe）的存在，甚至进一步划定各类草原亚型。本研究针对沿生态湿度梯度分布的欧亚东部草甸草原（meadow steppe）、典型草原（typical steppe）与荒漠草原（desert steppe）的现代花粉组合（pollen assemblages）进行了系统分析。花粉数据的多元排序分析结果显示，欧亚草原亚型可被清晰区分。不同草原亚型的区分主要依赖于花粉组合中的旱生组分。冗余分析（Redundancy analysis）表明，麻黄属（Ephedra）、柽柳属（Tamarix）、白刺属（Nitraria）及蒺藜科（Zygophyllaceae）的相对丰度与干旱程度呈正相关。麻黄属的相对丰度从草甸草原、典型草原至荒漠草原依次升高。柽柳属与蒺藜科仅见于典型草原与荒漠草原，未在草甸草原中检出。白刺属仅存在于荒漠草原。旱生组分的相对丰度在荒漠草原中高于典型草原。上述研究结果表明，基于现代花粉雨（pollen rain）可有效区分欧亚草原亚型。