Species interactions in three Lemnaceae species growing along a gradient
of zinc pollution
Abstract
Duckweeds (Lemnaceae) are increasingly studied for their potential for
phytoremediation of heavy-metal polluted water bodies. A prerequisite
for metal removal, however, is the tolerance of the organism to the
pollutant, e.g., the metal zinc (Zn). Duckweeds have been shown to
differ in their tolerances to Zn, however, despite them most commonly
co-occurring with other species, there is a lack of research concerning
the effect of species interactions on Zn tolerance. Here we tested
whether the presence of a second species influenced the growth rate of
the three duckweed species Lemna minor, Lemna gibba, and Lemna
turionifera. We used four different Zn concentrations in a replicated
microcosm experiment under sterile conditions, either growing the
species in isolation or in a 2-species mixture. The response to Zn
differed between species, but all three species showed a high tolerance
to Zn, with low levels of Zn even increasing the growth rates. The
growth rates of the individual species were influenced by the identity
of the competing species, but this was independent of the Zn
concentration. Our results suggest that species interactions should be
considered in future research with duckweeds and that several duckweed
species have high tolerance to metal pollution, making them candidates
for phytoremediation efforts.