Combined allelopathic effects of Spirogyra (Zygnematales: Zygnemataceae) and Ceratophyllum demersum (Ceratophyllales: Ceratophyllaceae) on the growth of Microcystis aeruginosa (Chroocolales: Microcystaceae)

Allelopathic inhibition activity of Spirogyra and Ceratophyllum demersum (C. demersum) on Microcystis aeruginosa were compared using a series of experiments. Culture solution of Spirogyra was found to inhibit growth of M. aeruginosa resulting in the destruction of chlorophyll-a and increased MDA content of the algae. The inhibitory effect was increased with greater concentrations of macrophyte culture solution and with continuous addition of the macrophytes. Filter size also had an effect in the inhibition of M. aeruginosa growth. Poor algal growth may have resulted from metabolic secretions from Spirogyra and associated epiphytic bacteria. Inhibition of algal growth and growth of the macrophytes and tolerance of Spirogyra to eutrophic conditions were further improved by synergistic effects of co-existing Spirogyra and C. demersum. Maximum inhibition effects and macrophyte biomass were recorded when the ratio of Spirogyra to C. demersum was 6:4.