Abstract:

Populus euphratica Oliv. is a beneficial species in desert riparian forests, and it plays an important role in maintaining the stability of desert riparian ecosystems and inhibiting desertification. To understand the variation patterns in Populus euphratica community structure and diversity characteristics along riverbanks in an extremely arid desert riparian area, the natural distribution of the Populus euphratica forest in the downstream desert riparian area of the Heihe River was selected as the observation sampling site, and 9 sites were vertically set along the riverbank to analyse the species composition, structure, flora and diversity characteristics of the Populus euphratica community along the river gradient. The results showed that the species diversity of the Populus euphratica community was low, with 9 species belonging to 7 families and 9 genera. Populus euphratica was the absolute dominant species in the community (the importance value was 0.61-0.90) and the dominant beneficial species. Plant flora was minimal, with a high proportion of single species families and genera, obvious temperate attributes, and a close geographical connection with ancient Mediterranean components. With increasing distance along the riverbank, the plant community structure transitioned from tree-shrub-grass to tree-grass. The coverage of the plant community increased and then decreased significantly, reaching a maximum of 74.33% 650 m away from the riverbank, and shrub layer coverage was generally lower than tree layer and herb layer coverage. The diversity indices of the Populus euphratica community were low, and the maximum values of the Patrick index, Simpson index, Shannon-Wiener index and Pielou index were 7, 0.66, 1.31 and 0.81, respectively. α diversity indices increased and then decreased along the river gradient, reaching a peak between 650-800 m away from the river, and the Pielou index did not change significantly. The Cody index peaked at 650-800 m and 800-950 m from the riverbank, while the Sørensen index was low. These results indicated that in this region, the β diversity of the Populus euphratica community was the highest, and the heterogeneity of the Populus euphratica community was high. In the downstream desert riparian area of the Heihe River, the variations in the soil water and salt limit and regulate the growth and distribution of herbaceous plants, which have an important influence on the community diversity of Populus euphratica forests. These results are helpful for understanding the community structure and diversity pattern of Populus euphratica along the Heihe river at the local scale and provide a scientific reference for the management and restoration of plant resources in the desert riparian Populus euphratica forest.

Key words: Populus euphratica Oliv., community structure, plant flora, diversity characteristics, river gradient

摘要：

胡杨（Populus euphratica Oliv.）是荒漠河岸林的主要建群种之一,对维持荒漠河岸生态系统稳定和抑制荒漠化有着重要意义。为科学认识极端干旱荒漠河岸地带胡杨群落结构、多样性特征沿河岸距离的变化规律,选择黑河下游荒漠河岸地带自然分布的胡杨林作为观测样地,沿垂直河岸方向上设置9个采样点,分析沿河梯度上胡杨群落物种组成、结构、植物区系与多样性特征。结果表明：在沿河梯度上,共有物种7科9属9种,物种多样性低,胡杨在群落中占绝对优势（重要值为0.61—0.90）,是群落优势建群种。植物区系贫乏,单种科和单种属占比高,具有明显温带属性,且与古地中海成分地理联系密切。随着沿河岸距离的增加,植物群落结构由乔-灌-草向乔-草类型过渡,植物群落盖度呈先上升后下降的显著变化趋势,在距河650 m处达到最大,为74.33%,灌木层盖度总体上低于乔木层和草本层。胡杨群落多样性指数偏低,Patrick指数、Simpson指数、Shannon-Wiener指数和Pielou指数最大值分别为7、0.66、1.31、0.81。α多样性指数随沿河岸距离的增加呈先上升后下降变化趋势,在距河650—800 m之间达到峰值,其中Pielou指数变化不显著。Cody指数在距河650—800 m和800—950 m之间出现较大值,而Sørensen指数较小,表明该区域β多样性最大,胡杨群落样地间异质性程度高。在黑河下游荒漠河地带,土壤水盐变化限制和调控着草本植物的生长和分布,对胡杨林群落多样性产生重要的影响。研究结果有助于认识该地区沿河胡杨群落结构特征及其多样性格局,也将为荒漠河岸胡杨林植物资源的管理和恢复提供科学参考。

关键词: 胡杨, 群落结构, 植物区系, 多样性特征, 沿河梯度