Does toxic Microcystis aeruginosa affect aquatic plant establishment?

Germination and establishment of aquatic plants in response to the addition of toxic and nontoxic cultures of Microcystis aeruginosa cells, the toxin, microcystin, or both nontoxic cells and dissolved microcystin was investigated in two glasshouse experiments and an in vitro germination experiment. The presence of high densities of cyanobacterial cells had a negative effect on aquatic plant establishment when cell densities were greater than 109 cells mL−1. Plants that were shaded with 20% shade cloth also had reduced establishment compared to the control. The most sensitive plants were species of Chara and Nitella. There was no evidence that dissolved microcystin (as cyanobacterial cell-free extracts) alone had a deleterious effect on aquatic plant germination and establishment. Dense cyanobacterial blooms may, therefore, have a role in preventing the establishment of aquatic plants through shading.