Root development is faster in common species of Potamogeton compared to declining species of Potamogeton in Danish lowland streams

The decline in biodiversity in freshwater ecosystems occurs at an alarming rate throughout the world. In Denmark, we know from historical records that several species within the plant genus Potamogeton, that were previously widespread in Danish freshwater ecosystems, are now under severe decline. In this study, we explore root development in two common and three declining Potamogeton species applying an experimental approach. Specifically, we examined if root development characteristics can contribute to explain the contrasting success of these species in the contemporary stream vegetation in Denmark. In accordance with our hypothesis, our results showed that common species of Potamogeton produced roots faster, had longer roots and produced more roots per growth node than declining Potamogeton species. This was particularly clear for P. crispus. Overall, our results expose a mechanism that is likely to affect the ability of these species to maintain populations in highly disturbed lowland streams in Denmark and therefore contribute to explain the contrasting success of these species.