Abstract: The effects of shrubs of Ephedra distachya and Artemisia arenaria on the distribution, species composition, species diversity and community structure of algae were investigated within and out of the shrubs of Ephedra distachya  and Artemisia arenaria . The results showed that there was no obvious difference in species composition of algae within and out of the shrubs of E. distachya and A. arenaria. The difference was mainly represented by the change of dominant species of algae. There was a difference of species diversity for the two semishrub plants. Species diversity in the shrubs of E. distachya was lower significantly than that out of the semishrubs. However, number of algal taxa in the semishrubs of A. arenaria was higher significantly than that out of the shrubs, and there was no difference in ShannonWeaver index. In community structure, number of taxa and dominance degree of cyanobacteria and filamentous algae in the semishrubs of E. distachya were significant lower than those out of the shrubs (P<0.05). An opposite change trend was observed for unicellular and coccoid algae. However, for A. arenaria, numbers of taxa of cyanobacteria, green algae, diatom, filamentous algae, unicellular and coccoid algae in the semishrubs were higher significantly than those out of the shrubs. The dominance degree of cyanobacteria and filamentous algae increased significantly from the internal area to the external area of the shrubs (P<0.01). An opposite trend was observed for green algae, unicellular and coccoid algae. The change of dominance degree of different communities within and out of the two semishrubs was mainly caused by some key taxa. Different distribution of algae in the semishrubs of E. distachya  andA. arenaria  was possibly caused by different regulative mechanisms.

Key words: Ephedra distachya, Artemisia arenaria, shrub, algae, species composition, species diversity, community structure, Gurbantonggut Desert