The strength of limiting factors for duckweed during algal competition

Abstract

Duckweed (Lemna gibba) growth was found to be strongly reduced by unicellular green algae (Scenedesmus conspicua, Chlorella sp., Chlamydomonas sp.) in indoor experiments. These algae reduced N, P, Fe and Mn concentrations of the medium drastically, moreover they increased the pH beyond 10. Subsequent additions of nutrients and pH neutralisation removed the growth inhibition of duckweed. This growth inhibition is, therefore, concluded to be due to pH increase and N, P and trace element (Fe, Mn) removal. Of the five factors significantly inhibiting duckweed growth, depletion of N was strongest, increase in pH was second, followed by reduction of P > Fe > Mn.