The effect of creosote on the growth of an axenic culture of Myriophyllum spicatum L.

Due to the importance of submersed, rooted macrophytes to the aquatic ecosy stem and the use of creosote impregnated structures adjacent to or within w ater bodies, a study was conducted using an axenic culture of Myriophyllum spicatum to determine the effect of creosote on this aquatic macrophyte. Fo ur plants were cloned and exposed to nominal creosote concentrations rangin g from 0.16 to 200 mg/l for 14 days. A variety of response parameters were assessed, including shoot and root length, number of roots and nodes, and d ry weight biomass, as well as visual observations on plant colouring and mo rphology. Regression and ANOVA analyses were conducted to determine EC50s a nd significant differences. Biphasic responses were observed for shoot leng th, node production and biomass, with shoot length showing statistically si gnificant stimulation (hormesis) at creosote concentrations below 13.3 mg/l . EC50 values of 55.1 (CI 40-60) mg/l, 33.4 (CI 26-48) mg/l and 86 (CI 70-1 20) mg/l were determined for shoot length, dry weight and node production, respectively. Root number was significantly higher at 3.6 mg/l and root len gth was significantly reduced at 4.5 mg/l creosote, within the concentratio n range that stimulated shoot growth. Visual changes, including an increase in pink colouration and changes in the location of root initiation, were a lso observed in the same creosote concentration range that affected root le ngth and numbers. Therefore, it appears that changes in root growth and loc ation of root initiation may be the most sensitive endpoints for creosote e ffects on Myriophyllum. (C) 2000 Elsevier Science B.V. All rights reserved.