Plasticity and rooting behaviour of Pontederia crassipes under vernal water level rise: Implications for biological invasion and management

As global warming continues, increasing minimum winter temperatures may no longer limit the northward expansion of invasive species, particularly those from tropical zones. A mesocosm experiment with a chronosequence approach (space-for-time trade-off) was used to examine the effects of water level variation on the traits of the invasive aquatic plant water hyacinth [ Pontederia crassipes (formerly Eichhornia crassipes )] collected from freezing, chilling and warm overwintering locations in China. We hypothesized that the phenotypic plasticity of the plant, particularly its ability to adjust its root morphology and topology in response to vernal water level rise, enhances its capacity to invade freshwater ecosystems. The results revealed significant plasticity in the response of the plants to water level, with plant traits such as total biomass, diaspore number, leaf area, specific leaf area, root length, and photosynthetic efficiency significantly increasing under a 10-cm water level, which can be regarded as a moderate overwintering water level. However, the plants from the warm location did not perform better than did those from the freezing or chilling locations, possibly because the harsh winter conditions reduced plant biomass but did not negatively affect the plants at the gene level. These findings highlight phenotypic plasticity in rooting behavior, which enables plant survival and growth during overwintering in the littoral zone, allowing P. crassipes to withstand low temperatures and to rapidly proliferate during the vernal water rise period. This study highlights the importance of early detection and management strategies to control the spread of P. crassipes , particularly given the trends in global climate change, which may facilitate its northward expansion. The use of P. crassipes as a model plant is recommended for studying the responses of invasive aquatic plants to global change in freshwater ecosystems.