Responses of five naturalised ornamental freshwater plant species to elevated carbon dioxide concentration and nutrient enrichment

Ongoing global environmental changes such as rising atmospheric CO₂ concentration ([CO₂]) and eutrophication are in some parts thought to facilitate exotic plant species invasions in freshwater systems. Although an increasing number of studies have documented the impacts of these factors on native and invasive freshwater plant species, relatively little is known about how they might interact to affect naturalised exotic species. We investigated the growth and biomass allocation responses of five naturalised ornamental freshwater plant species (Ludwigia palustris, Mentha aquatica, Mentha pulegium, Nasturtium officinale and Zantedeschia aethiopica) to varied levels of CO₂ (ambient and elevated) and nutrient (low and high) concentrations. We found limited evidence that these factors interacted to affect plant growth and biomass allocation. However, the relative growth rate (RGR) of most of the species was enhanced under elevated [CO₂] and/or nutrient enrichment. These results suggest that most of the tested study species will likely be of management concern under future global environmental change conditions. However, it is important that future research efforts test the potential shifts in the competitive interactions between native and exotic naturalised freshwater species in response to global environmental changes in order to determine community-level consequences of these changes.