Response of submerged macrophyte Ceratophyllum demersum to the exponential phase (EP) and declining phase (DP) of toxic Microcystis aeruginosa

The present work comprehensively investigated the responses of submerged Ceratophyllum demersum to exudates and extracts of toxic Microcystis aeruginosa at the exponential (EU, ET) or declining phase (DU, DT). The highest amount of MC-LR was detected in medium with DT, the value of which reached 6.36 mu g/l, and C. demersum exhibited the highest absorption of MC-LR with a value of 1.73 ng/g FW upon exposure to DU. Significant negative effects on C. demersum was detected under the treatment with EU of toxic M. aeruginosa, expressed with the reduction of freshweight, Chla/Chlb, and the Superoxide Dismutase (SOD) activity. Meanwhile, increased carotenoid/total chlorophyll ratio might be employed by submerged C. demersum as the defense strategy to EU of toxic M. aeruginosa. In addition, under EU treatment, the microorganisms Flavobacterium Bergey, and Chryseobacterium Vandamme, which exert negative effects on aquatic organisms, increased, whereas the Rhizobacter Goto & Kuwata, Limnothrix Meffert, and Pseudanabaena Lauterborn, which are beneficial to the growth of the plants, were lower. The research highlighted the significance of toxic cyanobacterial bloom development and different growth phases on submerged macrophytes, providing more insights for the allelopathic interaction between submerged macrophytes and toxic cyanobacteria in natural freshwater ecosystems.

Automated summary

This study comprehensively investigated the response of submerged Ceratophyllum demersum to exudates and extracts of toxic Microcystis aeruginosa at different growth phases and concentrations. The results showed that the effects on C. demersum varied depending on the growth phase and concentration, and the abundance of beneficial and harmful microorganisms was also affected.