This study aimed to determine the influence of different turbulence levels on morphologically different aquatic macrophyte species. The variations of growth and the alterations of indole acetic acid (IAA) and H 2 O 2 metabolism of three morphologically distinct aquatic macrophyte species, Elodea nuttallii, Potamogeton crispus and Vallisneria spiralis were studied in the exposure to three different turbulence conditions. Plants were subjected to turbulence generated by vertically oscillating horizontal grids at three different frequencies: 1, 2 and 4 Hz. A no-turbulence condition was used as a control. The growth of V. spiralis and E. nuttallii was suppressed by exposure to greater turbulence, though increased turbulence enhanced the growth of P. crispus. The growth rate of plants was positively correlated with IAA concentration. IAA concentration was negatively correlated with turbulence level in V. spiralis and E. nuttallii, while it was positively correlated in P. crispus. H 2 O 2 concentration was positively correlated with turbulence level in the former species, while it had no correlation in the latter. P. crispus showed more resistance to turbulenceinduced mechanical stress and growth suppression than the other two species. The observed variations of growth and IAA and H 2 O 2 metabolism showed that plant morphology has a significant influence on the response to flow turbulence. The results from this study provide a basis for understanding the mechanism and consequential morphological changes in plants that grow in moving water.

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The influence of flow turbulence on the growth of Chara fibrosa was studied for 12 weeks under laboratory conditions using a mechanically oscillating grid that generated turbulence without net flow. The experimental turbulence velocities were 1.93 AE 0.48 cm s À1 (high turbulence), 1.06 AE 0.41 cm s À1 (medium turbulence), and 0.46 AE 0.15 cm s À1 (low turbulence), while the control was a no turbulence condition. Plants exposed to high and medium turbulence showed shoot elongation rates less than 50% of the control throughout the experiment period. Ascorbate peroxidase activity and catalase activity were elevated, and reductions of total chlorophyll content and photosynthetic efficiency were observed in the plants exposed to turbulence. Carbon content of the plant tissue was decreased in the high and medium turbulence treatments; in contrast, it was slightly increased in the treatment of low turbulence. Exposure to turbulence adversely affected growth of C. fibrosa, though all the plants survived the experiment period.

-Exposure to water movement has been observed to alter various processes in the plants including growth, hormone concentration and nutrient uptake. In the current study, Chara fibrosa was exposed to three different turbulence conditions and compared with a control. Turbulence was generated in the laboratory by using a vertically oscillating grid setup. Exposure to turbulence caused a reduction in shoot length and nutrient uptake in C. fibrosa. Variation of stable isotope composition was measured as a surrogate variable that is able to integrate variations of many physiological processes. It was initially hypothesized that the reduction of diffusion boundary layer around the plant will increase isotopic discrimination against 13 C and 15 N, when exposed to increasing turbulence. Although the results generally agree with the hypothesis, a trend of increment was observed in d 13 C in the plants exposed to turbulent velocities from 0.46 to 1.93 cm s x1 , against the hypothesis. Mechanical stress induced reduction of carbon uptake and lipid peroxidation due to the development of oxidative stress may be the reasons behind the above-mentioned trend. The study exhibits that the net effect of physical and physiochemical changes of the plants was displayed in d 13 C signatures and it is important to consider physical conditions of the local environment, in using stable isotope signatures for ecosystem studies.