Effects of the aquatic extracts of Arundo donax L. on the growth of freshwater algae

In recent years, a novel and environment-friendly method to control algal blooms based on allelopathic inhibition of macrophytes on algae has drawn much attention. We studied the effects of aquatic extract of Arundo donax L. (giant reed) on the growth of four freshwater algae [bloom-forming toxic cyanobacterium (Microcystis aeruginosa) and green algae (Selenastrum capricornutum, Scenedesmus obliquus, and Chlorella pyrenoidosa)] to control algal blooms. In bioassays, giant reed extract inhibited the growth of M. aeruginosa and its cell size was reduced with increase in extract concentration. However, the extract stimulated the growth of both S. capricornutum and S. obliquus. Most spindle-shaped cells of S. obliquus turned into rotundity, i.e. cell polarity was destroyed by the extract. The extract had a variable effect on the growth of C. pyrenoidosa. In the prophase of incubation, the cells of C. pyrenoidosa treated with the extract were significantly larger than control. Thus allelopathic effects of extract of A. donax L. on algae were strain-specific and A. donaxL. may control the toxic cyanobacterium M. aeruginosa.