Eurasian watermilfoil (Myriophyllum spicatum) alters its root topology but conserves its root branching in response to freshwater cultural eutrophication

Abstract

Cultural eutrophication is the main cause of the decline of submerged plants in freshwater ecosystems. While many studies have focused on the nutrient uptake by the roots of these plants, less attention has been given to the effects of eutrophication on root structure. We designed a mesocosm experiment with Eurasian watermilfoil (Myriophyllum spicatum), a submerged plant indigenous to the Eurasian continent. The responses of plant functional traits, including growth traits, morphological traits and root topological indices, to different nitrogen (N) and phosphorus (P) concentrations were elucidated. We found that high P concentrations suppressed all the morphological traits and reduced the root topological traits, whereas N concentrations had a comparatively minor effect. Although the root branching of M. spicatum did not change, its root topology became more dichotomous with fewer exterior root links being formed in nutrient-rich habitats, and the root form changed from deep and thin to shallow and dense with increasing P concentrations. The root nutrient absorption ability of M. spicatum may decrease with cultural eutrophication, and this change most likely reduces its anchoring ability and increases its sensitivity to dislodge from the sediment if disturbed by hydraulic forces.