Sofia Vamos, Sofia Julia van Moorsel 

Duckweed, a widely distributed aquatic plant family, are economically important and have high potential for phytoremediation of polluted water bodies. We collected four Lemna gibba/minor populations from across Switzerland and assessed how their original vs. foreign environments influenced their growth. Additionally, we investigated their response to a metal pollutant (Zn) in both the original and foreign environment. Zn is found in freshwater systems and can become harmful at elevated concentrations. We hypothesized that growing in their original environment would help the plants buffer the negative effect of the metal pollutant.
To test this, we measured Lemna growth in a reciprocal transplant experiment in a glasshouse where the four plant populations were grown in each of the environments, as well as in three different concentrations of Zn. We sampled chlorophyll-a as a proxy for algal biomass, and also measured total nitrogen and total organic carbon.
The four Lemna gibba/minor populations exhibited significantly different growth rates across environments. However, the effect of the environment on duckweed growth was the same for all populations. We did thus not find evidence for local adaptation, and instead observed strong plastic responses in the populations. Zn increased duckweed growth rate but inhibited algal growth. Consequently, the positive effect of Zn on duckweed growth could be in part via reducing the competition with algae. We conclude that L.gibba/minor ecotypes may exhibit large differences in growth rate but that the species overall has a high Zn tolerance and strong plastic adaptive potential in novel environments.