effective concentrations against bacteria and fungi were 2–3 orders of magnitude higher
than we found against cyanobacteria and algae and one order of magnitude higher than D.
magna and L. minor.
These data confirm our results that C. majus features a selective toxicity to
phytoplankton species in comparison with L. minor and D. magna as representatives of
sensitive non-target aquatic organisms. Because C. majus showed significant selective
inhibition properties to algae and cyanobacteria, it was also tested with a natural
phytoplankton community under environmental conditions (medium, temperature, light–
dark cycle). In this experiment we noted a slightly lower toxicity of the C. majus extract
toward the natural phytoplankton as compared with laboratory cultures of cyanobacteria and
algae. The low toxicity was possibly the result of adaptation of natural phytoplankton
species to environmental pollution with lower sensitivity in comparison with laboratory
cultures, microbial degradation of active compounds from the extract, or secondary to
interactions with chemicals dissolved in natural water. High dominance of green algae over
cyanobacteria and diatoms at the end of the experiment was probably caused by their higher
growth rates.