CO2 availability rather than light and temperature determines growth and phenotypical responses in submerged Myriophyllum aquaticum

The impact of light, temperature and carbon on growth, phenology and pigment content has been studied in submerged Myriophyllum aquaticum (Vell.) Verdc. Applying a three-level factorial experimental design (light × temperature × carbon), we show that dissolved inorganic carbon resp. CO2 acts as the major trigger for plant acclimation. Changes in carbon availability induced the most pronounced significant differences with respect to relative growth rate, dry matter content, and the length of internodes, compared to the effects of light and temperature. The dry matter content of leaves, stems, and roots was significantly affected by carbon, while light and temperature played only a minor role. Biomass distributions in roots, shoots and leaves were most significantly affected by temperature, and the length of internodes was significantly influenced by temperature, light and carbon. Effects of the tested variables on pigment content have been found for the total chlorophyll content, which was significantly influenced by light and carbon, and the chlorophyll a:b ratio, which was affected by temperature and carbon. In summary, our data support a high phenotypic plasticity of M. aquaticum, which is largely dependent on carbon availability. This high phenotypic plasticity might be one of the reasons for the success and invasiveness of this species in a wide range of aquatic habitats.