Higher resistance of a microcystin (MC)-producing cyanobacterium, Microcystis to the submerged macrophyte Myriophyllum spicatum

Abstract Microcystin (MC) -producing and non-MC-producing Microcystis strains typically coexist in Microcystis -dominated blooms. However, the interaction between submerged plants and Microcystis at strain level is not clear. This study aimed to assess the effects of a submerged macrophyte Myriophyllum spicatum on one MC-producing versus one non- MC-producing strains of the cyanobacterium Microcystis using plant- Microcystis co-culture experiments. The impacts of Microcystis on M. spicatum were also examined. It showed that the MC-producing Microcystis strain had a higher resistance to negative impacts by the cocultured submerged plant M. spicatum than the non-MC-producing strain. By contrast, the plant M. spicatum was impacted more by the MC-producing Microcystis than the non-MC-producer. The associated bacterioplankton community was affected more by the MC-producing Microcystis than the cocultured M. spicatum . The MC cell quotas were significantly higher in the coculture treatment (the PM+ treatment, p < 0.05), indicating that the production and release of MCs might be a key factor responsible for the reduced impact of M. spicatum . The higher concentrations of dissolved organic and reducing inorganic compounds might eventually exacerbate the recovering capacity of co-existing submerged plants. Overall, this study indicated that the capacity to produce MCs, as well as the density of Microcystis should be taken into account when attempting to re-establish submerged vegetation to undertake remediation works.