The effect of flow turbulence on growth, nutrient uptake and stable carbon and nitrogen isotope signatures inChara fibrosa

Abstract

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 diffu- sion 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.