The influence of fragmentation on the growth of Elodea canadensis Michx. in different light conditions

Plant fragments are commonly noticed in a wide range of freshwater environments. However, data on their further growth remain very scarce. The post-fragmentation growth of Elodea canadensis was analysed in a laboratory experiment in which plants were exposed to different light conditions ranging from 3 to 30 µmol m⁻² s⁻¹. The growth of whole plants (12cm) and fragmented (cut) shoots (apical fragment of 3 cm and middle and lower fragments of 4 and 5 cm respectively) was analysed over 33 days (with measurements of weight and length after 11, 21 and 33 days). In all light treatments both cut and whole plants grew. The growth rates were found to vary greatly over the exposure period. During the first 11 days, whole plants or the fragments thereof exhibited the greatest increases in biomass and length in all light treatments. Following further exposure under no shade and moderate shade, the growth of all plants, although still significant, was visibly more limited. Under conditions of a 90% shade level, 11 days of exposure left both whole and cut plants still alive, but incapable of any further significant increase in length or biomass. Generally, in high light levels cut plants grew more intensively, while in conditions of the most intensive (90%) shade, no differences in growth of these groups of plants were noted or the growth of cut plants was limited to a greater extent. A greater number of new lateral shoots were noted in cut plants than in whole plants. Even in conditions of low light characterized by the poor growth of plant fragments the production of new shoots was still possible. In general, fragments of Elodea canadensis were found to be very efficient at surviving and regenerating under a wide range of light conditions.