Abstract: Aim Ephemeral rivers are important ecological corridors and biological refuges in arid regions, but the interactive effects of elevation and ephemeral rivers on plant community structure and distribution in arid regions remain unclear. Therefore, this study focuses on the West Tugou and Daquan River basins within the Dunhuang Basin in the arid region of Northwest China. It investigates the differences in individual plant size, species distribution, and community structure inside and outside the ephemeral rivers, and explores whether there are interactive effects between ephemeral rivers and elevation gradients on plant communities. Method The Mann–Whitney U test was used to compare the differences in plant community characteristics between the upstream and downstream of the ephemeral river. A multi-level mixed-effects model was employed to analyze and investigate the interactive effects of the river and altitude on the plant community. A generalized additive model was utilized to identify the nonlinear characteristics of the altitude response. The Wilcoxon signed-rank test was used to assess whether there was a significant shift in the upper and lower limits of the distribution of common species. Important findings 1) The ephemeral river broke through the vertical zonation distribution of species under the water and heat limitations of the arid area. It not only increased the number of species (the total number of species within the river was 1.9–2.7 times that of the outside), but also significantly reduced the lower limit of species distribution in the river channel (p < 0.05) for the Xitugou river. The Daquan River also showed a downward trend, but the upper limit of species distribution in both river basins did not show a comprehensive upward movement. 2) The Mann-Whitney U non-parametric test showed that the average plant height and crown width inside both rivers were significantly higher than those outside (p < 0.05). In the West Tugou area, vegetation coverage was significantly greater inside the river than outside (p < 0.05), whereas in the Daquan River area, plant density was significantly greater outside the river than inside (p < 0.05); other community characteristics showed no statistically significant differences. 3) As the altitude increases, the average height and average canopy width of plants inside and outside the river decrease, while the vegetation coverage and plant density increase. Moreover, the decrease or increase in the river area is more significant. 4) The mixed effect model indicates that altitude and river location jointly drive the changes in vegetation coverage, plant density, and community structure. The average height is mainly influenced by altitude, reflecting the nonlinear regulation of hydrological and geomorphic processes on community formation in different altitude zones.

Key words: Arid zone, Ephemeral river, Altitude, Species distribution, Plant community structure