Water blooms in eutrophic waters have been serious environmental problems in recent years. To explore
effective measures to control this issue has been an interest of research. Our current study was designed
to investigate the effects of submerged macrophyte Najas minor All. exudates on the growth of
four freshwater phytoplankton species, toxic Microcystis aeruginosa, toxic Anabaena flos-aquae, Chlorella
pyrenoidosa and Scenedesmus obliquus as well as natural phytoplankton assemblages of pond water. We
also conducted a reciprocal response between N. minor and toxic M. aeruginosa using coexistence experiments.
Our results showed that: (1) N. minor exudates significantly inhibited the growth of toxic
M. aeruginosa, toxic A. flos-aquae and S. obliquus, with M. aeruginosa being the most sensitive, followed
by toxic A. flos-aquae, and S. obliquus the least. N. minor exudates did not show inhibitory effect on
C. pyrenoidosa; (2) N. minor and toxic M. aeruginosa have reciprocal inhibitory effect, and the allelopathic
interactions between the two different organisms are density dependent and affect their mutual
growth; (3) N. minor exudates also can induce a decrease in chlorophyll a content and an inhibition in
total dehydrogenase activity of the phytoplankton assemblages. Our present studies indicated the submerged
macrophyte N. minor might be a potential useful tool to control phytoplankton blooms.