| Abstract: | The duckweeds Lemna gibba L. and Lemna minor L. only grew wellin undisturbed culture under axenic conditions in low lightintensity when provided with a suitable energy source such asglucose. In media containing N03-N gibbosity (a convex ventralsurface) was induced in the presence of the chelating agentethylene-diamine-di-o-hydroxyphenylacetic acid (EDDHA). In nutrientsolutions containing NO3-N as the only N source, but withoutEDDHA, L. gibba occasionally exhibited gibbosity in culturesolutions of 40 cm3 volumes. More fronds were induced to exhibitgibbosity when the volume of the culture medium was increasedfrom 40 cm3 to 200 cm3. Gibbosity was never induced in L. minor,neither was it induced in L. gibba in media containing NH4-N,even in the presence of NO3-N. There was no direct correlationbetween the occurrence of gibbosity and frond growth rate, butgibbosity occurred only when there was good frond growth. In the absence of a sugar, frond growth was enhanced by bubblingair through the culture solution in the light. Increasing theCO2 concentration in the air up to 1% enhanced growth and inducedgibbosity. Carbon dioxide did not induce gibbosity in mediacontaining NH4-N. Key words: Ammonium-N, carbon dioxide, gibbosity, Lemna, nitrate-N |
