Allelopathic effects among selected species of phytoplankton and macrophytes

Abstract

Aim: To understand the allelopathy among different taxonomic levels of freshwater photoautotrophs, the effect of aqueous extracts of Phragmites australis and Schoenoplectus californicus on monocultures of Microcystis aeruginosa and Scenedesmus acutus was investigated. In addition, the cell extract and filtered medium of each phytoplankton species were used and tested between them. Methodology: In the macrophyte bioassays against alga, the allelopathic effect was evaluated separately using 10 and 20 mg of aqueous extract of leaf, stem and rhizome of Phragmites, as well as the stem and rhizome of Schoenoplectus. In the assays between the phytoplankton species, the cell extract (12.44 ± 0.16 μgl-1 microcistin-LR equivalents) and the filtered culture medium (2.98 ± 0.03 μgl-1 microcistin-LR equivalents) of Microcystis were used in 100 and 50% and were added to the Scenedesmus monocultures. In the same proportion, the cell extract and the filtered culture medium of Scenedesmus on monocultures of Microcystis were used. Results: In Phragmites, leaf extract showed greater inhibition activity than the other plant organs on Microcystis cultures. The stem and rhizome showed a larger decrease for the growth of Scenedesmus cultures. For Schoenoplectus, the stem extract showed a greater inhibitory effect than the rhizome extract; this was observed on both alga and cyanobacteria. Microcystis when in contact with the cellular extract of Scenedesmus, it was observed that the bioactive containing substances in the extract had a greater inhibitory activity. Interpretation: The leaf, stem and rhizome extracts of Phragmites and Schoenoplectus showed a different affinity of the allelopathic activity on Microcystis and Scenedesmus, suggesting a species-specific relationship.