Submerged plant allelopathic effects on the growth of a harmful bloom-forming cyanobacterium (Microcystis aeruginosa): a diversity gradient experiment

Context Although it is well known that aquatic plants have allelopathic effects on phytoplankton, the allelopathic effects of differing diversities of aquatic plants on phytoplankton are not well known. Using diverse mixed submerged plant allelopathy to control cyanobacteria may be a potential strategy for eutrophic aquatic ecosystems. However, previous studies have mainly focussed on the allelopathic effects of few macrophytes on algae, and studies on the allelopathic effects of a differing diversity of submerged plants on cyanobacteria are rare. Aims To determine the allelopathic effects of submerged plants at different diversities on cyanobacteria. Methods We determined the allelopathic effects of four submerged macrophytes along a diversity gradient on the growth of a bloom-forming alga, Microcystis aeruginosa. Key results The results showed that the algal density, algal growth rate and chlorophyll-a concentration were negatively affected by plant exudates. Moreover, the algal growth inhibition increased with submerged plant diversity. Additionally, the algal growth inhibition caused by Ceratophyllum demersum was the most significant among the four species. Conclusions These results indicated that submerged plants had obvious allelopathic effects on the growth of M. aeruginosa, and the allelopathic effects increased with species diversity. Implication Accordingly, using diverse mixed submerged plant allelopathy to control cyanobacteria is an alternative potential strategy in eutrophic aquatic ecosystems. However, the effects of submerged plant allelopathy on other aquatic organisms and water quality need to be further studied to ensure its safety.