Egeria densa Allelopathy on Microcystis aeruginosa Under Different Light Intensities and Preliminary Insight into Inter-Parameter Relationships

Abstract

Egeria densa release allelochemicals harmful to other species, including cyanobacteria. Under natural conditions, E. densa and Microcystis aeruginosa can be found in various aquatic systems with different light levels. The effect that the coexistence of E. densa has on M. aeruginosa was tested under different photosynthetically active radiation (PAR) intensities. The growth, chlorophyll-a, oxidative stress, and antioxidant activities of M. aeruginosa were quantified after 7 days of coexistence with E. densa. A control experiment without E. densa was conducted for M. aeruginosa under the same conditions to distinguish the effect of the PAR intensity from the allelopathic effect. The allelopathy of E. densa on M. aeruginosa is significantly influenced by the PAR intensity. PAR intensities lower or higher than the favorable range further suppressed M. aeruginosa under coexistence. Research has revealed that the allelopathic effect of E. densa can be utilized to biologically suppress M. aeruginosa under various light conditions. Strong second-order polynomial distributions between the optical density (OD) and cellular H2O2 content of M. aeruginosa were found for both the control and coexistence conditions. In the practical application of E. densa allelopathy, OD can be adopted as a convenient method to obtain an approximate stress status on M. aeruginosa.