A simple method for analysing the effects of algae on the growth of Lemna and preventing algal growth in duckweed bioassays

A simple novel method for indoor culture experiments with small floating water plants, such as Lemnaceae, is described. Experiments demonstrate that the method allows for longer lasting culture experiments with Lemna, avoiding algal growth and self-shading of fronds by overcrowding. This is achieved by enclosing the Lemna fronds in tubes, which are replaced during growth by tubes of increasing diameter. The RGR of Lemna reached optimal values (RGR >0.3 day(-1)) when not hampered by algal growth. In competition experiments with algae growing outside the tubes and Lemna inside the tubes, the growth of the fronds decreased dramatically; chlorophyll content of the fronds was 91-97 % less and RGR 29-55 % less. This method allows for multifactorial experiments, handling up to 100 experimental units per researcher. This paves the road to competition experiments among and between water plants for light, nutrients and space.