Influence of nutrients on the development of gibbosity in fronds of the duckweedLemna gibbaL.

The duckweeds Lemna gibba L. and Lemna minor L. only grew well in undisturbed culture under axenic conditions in low light intensity when provided with a suitable energy source such as glucose. In media containing N03-N gibbosity (a convex ventral surface) was induced in the presence of the chelating agent ethylene-diamine-di-o-hydroxyphenylacetic acid (EDDHA). In nutrient solutions containing NO3-N as the only N source, but without EDDHA, L. gibba occasionally exhibited gibbosity in culture solutions of 40 cm3 volumes. More fronds were induced to exhibit gibbosity when the volume of the culture medium was increased from 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 correlation between the occurrence of gibbosity and frond growth rate, but gibbosity occurred only when there was good frond growth. In the absence of a sugar, frond growth was enhanced by bubbling air through the culture solution in the light. Increasing the CO2 concentration in the air up to 1% enhanced growth and induced gibbosity. Carbon dioxide did not induce gibbosity in media containing NH4-N.