Abstract
The present study systematically explored the purification effects and response of submerged plants, Ceratophyllum demersum and Myriophyllum spicatum, on toxic and non-toxic strains of Microcystis aeruginosa via indoor co-culture experiments. The results showed that: (1) Both plants significantly inhibited the growth of Microcystis and reduced the concentration of chlorophyll-a (Chla) in the water by rapidly absorbing nutrients such as nitrogen and phosphorus, with no significant differences in the inhibition between toxic and non-toxic strains, indicating that nutrient competition might be the dominant mechanism for algal suppression. (2) C. demersum had higher nitrogen and phosphorus removal efficiency than M. spicatum, but the microcystins (MCs) released by toxic M. aeruginosa inhibited the nutrient removal capacity of both plants. (3) The plants promoted cell lysis of toxic M. aeruginosa and reduced extracellular MCs in the water while accumulating MCs internally, with C. demersum showing stronger MC accumulation and removal ability. (4) Microcystis stress activated the plants' antioxidant defense systems, increased activities of SOD (Superoxide Dismutase) and CAT (Catalase), and caused membrane lipid peroxidation, increased content of MDA (Malondialdehyde), with toxic M. aeruginosa inducing stronger oxidative stress, and M. spicatum being more severely affected. (5) Plant species and algal toxicity jointly drove changes in the attached microbial community structure. The rhizosphere of M. spicatum specifically enriched Bdellovibrionota, suggesting a potential microbial predation pathway for algal suppression, while C. demersum was more associated with Bacillus and other microbes with allelopathic potential. In summary, C. demersum performed better in nutrient removal, toxin accumulation, and physiological tolerance. This study provides further theoretical support for using submerged plants to regulate cyanobacterial blooms and remediate eutrophic water bodies.