Inhibitory effect of invasive aquatic plants on common algae bloom species and the underlying physiological mechanisms.
To utilize the resource of invasive aquatic plants and reduce their harm to the environment, three typical invasive aquatic plants (Pistia stratiotes, Eichhornia crassipes and Alternanthera philoxeroides) were chosen as the study objects to investigate the influences of their two different allelopathy ways (algae-inhibition respectively by planting water and crude extract) on the growth of three common algae bloom species (Chlorella pyrenoidosa, Cyclotella meneghiniana, Microcystis aeruginos), and the underlying physiological mechanisms of algae-inhibitory was also investigated. The experimental results indicate that both the planting water and crude extract of the three plants showed selective algae-inhibitory effect on different microalgae, and the algae-inhibitory effects of planting water were overall stronger than the crude extract. Furthermore, the A. philoxeroides planting water had the strongest inhibitory effect on M. aeruginos and the OD750 of algal cells decreased by 73.09% and the content of chl a decreased by 96.61% on the 7th day of co-culture. Under the influence of A. philoxeroides planting water, the respiration rate of M. aeruginos increased firstly and then decreased. The photosynthetic rate decreased gradually, while the activities of antioxidant enzymes (SOD, POD, CAT), protein content, and malondialdehyde (MDA) content increased firstly then decreased, which indicated that M. aeruginos was subjected to coercion and injury obviously during the entire culturing period. However, the total amount of microcystins (MCs) in the experimental group increased by only 8.69% more than that of the blank group (P<0.05) on the 11th day of co-culture. Therefore, it can be concluded that the application of A. philoxeroides planting water has a high degree of ecological safety and can be adopted in practical control of algae blooms, because it can effectively inhibit the growth of M. aeruginos without increasing the release of cyanotoxins.