中国草原区主要群落类型花粉组合特征

Pollen assemblages of major steppe communities in China

现代表土花粉组合与植被关系研究是推断过去植被演化的基础。对中国草原区 39个样点进行植被调查及表土花粉分析的研究结果表明 ,表土花粉组合可反映出草原植被的总体特征。大多数样品中乔木花粉百分比低于 5 %。蒿属、藜科是草原区所有样品花粉组合中最主要的成分 ,两者在花粉组合中所占比例多大于 5 0 % ,且人类活动越强或气候越干旱 ,蒿属、藜科花粉所占百分比越高。花粉组合不能反映群落结构特征 ,如建群种、结构、盖度等的差异在花粉组合中表现不出来。即使以禾本科为建群种的草原群落 ,禾本科花粉所占比例也多低于 10 %。花粉浓度在草原区花粉与植被关系研究中意义不明确。典型草原与荒漠草原花粉组合存在明显区别 ,无倾向性对应分析 (DCA)分析表明 ,典型草原区样品在第一排序轴的排序值多高于 0 ,荒漠草原区样品的排序值小于 0 ;典型草原区藜科花粉百分比一般低于 2 5 % ,花粉类型多样性指数大于 2 ,当蒿藜占花粉总数的 5 0 %以上时 ,蒿藜比值大于 2。荒漠草原区藜科花粉含量多高于 2 5 % ,蒿藜比值多为 0 .5～ 2 ,花粉类型多样性指数多为 1～ 2。蒿属花粉属超代表性 ,但在蒿类建群的群落中 。

Relationships between modern surface pollen and vegetation are essential for recovering past vegetation. In this paper, 39 sites covering various types of steppe in China were selected to study the relationships, at each sites, one surface soil sample was collected and vegetation investigations were carried out at the same time. The result shows that surface pollen assemblages reflect similar characteristics for all types of steppe vegetation in general. The percentages of arboreal pollen are less than 5% in most of samples, with Artemisia and Chenopodiaceae as the most important pollen types. The percentages of Artemisia and Chenopodiaceae are more than 50% in most of the samples and increase with aridity or under the impact of human. However, the surface pollen assemblages do not reflect the structure and cover of plant communities. The percentages of Gramineae are less than 10% in surface pollen assemblages even in areas where Gramineae is the constructive or dominant species in plant communities. This indicates that total pollen concentration is not an essential factor for studying the relationships between surface pollen and vegetation. The surface pollen assemblages also show some differences between typical steppe and desert steppe. Based on Detrended Correspondence Analysis (DCA), the ordering values of samples in typical steppe areas were less than zero in the axis one, while the ordering values of samples from desert steppe areas are more than zero in the same axis. In pollen assemblages of typical steppe, the percentages of Chenopodiaceae are less than 25%, and pollen types diversity indices are more than 2, and the ratio between Artemisia and Chenopodiaceae (A/C) are more than 2 when Chenopodiaceae and Artemisia are more than 50%. In pollen assemblages of desert steppe, the percentages of Chenopodiaceae and Artemisia are more than 60% and Chenopodiaceae are more than 20%; pollen types indices are 1～2, and A/C values are 0.5～2. Although Artemisia are often considered as over-representative pollen types, the percentages of Artemisia in pollen assemblages are found less than that in vegetations when Artemisia become constructive species and the percentages of Gramineae are less than 10% in steppe vegetations.