Sucrose modifies growth and physiology in axenically grown Myriophyllum spicatum with potential effects on the response to pollutants.

Sucrose as carbon source in axenic tests affects plant growth and physiology. We postulate that the high sucrose concentration in the OECD TG238 for the submerged growing aquatic plant Myriophyllum spicatum may modify pollutant effects, thus impairing environmental risk assessment. In a factorial design experiment with axenic M. spicatum exposed to three sucrose concentrations (no, low and high) with or without cadmium, we measured growth, dry matter content (DMC), content in pigments or phenolic compounds, and elemental stoichiometry of carbon, nitrogen and phosphorus. We show that sucrose is crucial for growth, but can be used at lower concentrations than currently considered. Sucrose-treated plants had higher DMC and carbon content, but lower contents in chlorophyll and nitrogen. Cadmium affected the content in chlorophyll, phenolic compounds, and elemental stoichiometry. Interactive effects were observed on length growth, the carbon and nitrogen content and the C:N and N:P molar ratios. Remarkably, cadmium led to increased shoot length at low but not at high sucrose concentration. This contrasting effect might result from differences in osmotic potential caused by sucrose. Overall, we found a strong effect of sucrose concentration on the growth and physiology of M. spicatum, and modifications of the response to cadmium. Further studies should establish the lowest sucrose level needed to account for realistic environmental risk assessment based on the axenic OECD TG238. This article is protected by copyright. All rights reserved