THE INFLUENCE OF SUBSTRATUM AND WATER VELOCITY ON GROWTH OF RANUNCULUS-AQUATILIS L (RANUNCULACEAE)

This study investigated the combined influence of three different flow velocities (high, 22.6 cm s-1; medium, 11.0 cm s-1; low, below 2 cm s-1) and substrata (mud, sand and gravel) on the growth of Ranunculus aquatilis L. (measured as the ratio between the final and initial wet weight of plant shoots kept in wood boxes in the stream for 21 days). The results showed highest levels of growth in mud substrate at all velocities (1.5-3.9 times higher than in sand and gravel). Highest growth for plants in sand and gravel was observed at medium velocity. In sand, this was about 1.6-2.8 times higher than growth at low or high flows. In gravel, growth was about 1.2 times and 1.6 times higher than at low and high velocities, respectively. The experiment indicates that the substratum and water velocity have a combined influence on the growth of R. aquatilis, and that the relative importance of each depends on the interactions of the particular substrata and velocities. The specific mechanisms involved in this influence have not been determined, but it is suggested that both the nutrient content and the texture of the substratum play important roles.