Does translocation influence growth or invasiveness of clonal cattail (Typha) species?

Background/Question/Methods

Freshwater coastal wetland plant communities provide many valuable ecosystem services, but are also prone to invasion by non-native plants that may influence the ecological function of the plant community.  Many wetland plant invaders are highly clonal, but how clonality affects the probability or rate of wetland invasion by non-native species is not well understood.  In particular, little is known about how translocation of stored resources affects the probability or rate of invasive spread.  We tested whether translocation of resources from rhizomes affected the probability of establishment or rate of growth of three cattail taxa (one native and two non-native) in the Laurentian Great Lakes region of North America.  We planted Typha latifolia, T. angustifolia, and T. X glaucaclonal fragments of variable sizes at very low densities in a common garden experiment and measured their survival and growth over two years.

Results/Conclusions

Growth of entire clonal fragments during the first month of the experiment was most strongly related to the initial maternal stem height (p < 0.01), but this effect subsequently diminished later in the season when growth rate was more strongly related to initial rhizome size (p < 0.001).  However, by the beginning of the second growing season both of these effects were strongly diminished, and by the end of the second year, total biomass of a clone was unrelated to initial size of the fragment.  These results suggest that resources remobilized from the maternal stems or rhizomes provide an initial subsidy for clonal expansion, but this effect diminishes over the long term.  Maternal subsidies were larger for the exotic taxa T. angustifolia and T. X glauca than for the native T. latifolia, suggesting that translocation differences between taxa may help explain the invasiveness of the exotic taxa.  There were also differences between exotic and native taxa at the individual ramet level; the growth of native T. latifolia ramets depended only on the size of the parent ramet immediately adjacent to it, while the growth of ramets for both exotic taxa depended on the size of three or more adjacent ramets.  While overall growth of the three taxa was quite similar, the two non-native cattail species did accrue slightly more biomass than the native T. latifolia (p = 0.043).  Together, these results suggest that taxon-specific differences in translocation may play a role in the invasiveness of non-native Typha taxa.