Growth of Elodea canadensis and Elodea nuttallii in monocultures and mixture under different light and nutrient conditions

Elodea canadensis and Elodea nuttallii were used in indoor experiments to compare their survival and growth in monocultures and mixture, (1) under different light intensities and (2) in water enriched or not enriched with phosphate. In all cases, E. nuttallii grew better than E. canadensis. The growth of E. canadensis was affected by a reduction in light intensity, contrary to that of E. nuttallii. Increasing phosphate-content of water did not affect the stem elongation of Elodea species, but increased the growth rate of E. nuttallii calculated on dry weight. It is hypothesised that the formation of a canopy of E. nuttallii shading E. canadensis is a key factor in explaining the success of E. nuttallii in the field particularly under eutrophic conditions, differences in nutrient uptake between the two species being of secondary importance.