Effects of Toxic and Non-Toxic Microcystis aeruginosa on the Defense System of Ceratophyllum demersum–Scenedesmus obliquus

The effects of toxic and non-toxic <i>Microcystis aeruginosa</i> on the <i>Ceratophyllum demersum</i>-<i>Scenedesmus obliquus</i> system were simulated in the laboratory, and some parameters in relation to these organisms were measured. In this experiment, <i>C. demersum</i> increased the biomass of <i>S. obliquus</i>, and both toxic and non-toxic <i>M. aeruginosa</i> significantly inhibited the colony formation of <i>S. obliquus</i> and inhibited the promotion of <i>S. obliquus</i> biomass. On the 14th day, the soluble polysaccharide content of <i>C. demersum</i> decreased when it was coexisted with <i>S. obliquus</i>, but it rose again because of <i>M. aeruginosa</i>, which significantly increased the protein content of <i>C. demersum</i>. The species composition and diversity of epiphytic microorganisms also vary with different treatments. Proteobacteria is dominant in all the groups, especially in the Toxic_SMC group. In addition, bacteria that can degrade organic pollutants are more abundant in Toxic_SMC group. This study focuses on the defense response of <i>S. obliquus</i> induced by <i>C. demersum</i> under the pressure of toxic or non-toxic <i>M. aeruginosa</i> and evaluates the changes to <i>C. demersum</i> and its epiphytic microorganisms, which provides insights for the study of aquatic plant-algae integrated action systems in eutrophic or cyanobacterial blooms.