Szabó S. et al. Phenotypic plasticity as a clue... (2018)

Szabó, S., Peters, E., Roijackers, R., Várbíró, G., Borics, G. & Lukács, B.A.
Phenotypic plasticity as a clue for the invasion success of the submerged aquatic plant Elodea nuttallii
PLANT BIOLOGY 21: 54–63.
Angol nyelvű összefoglaló: 

Two closely related alien submerged aquatic plants were introduced in Europe. The new invader (Elodea nuttallii) gradually displaced E. canadensis even at sites where the latter was well‐established. The aim of the study was to evaluate the combined effects of environmental factors on several phenotypic characteristics of the two Elodea species, and to relate these phenotypic characteristics to the invasion success of E. nuttallii over E. canadensis.
In a factorial design, Elodea plants were grown in aquaria containing five different nitrogen concentrations and incubated at five different light intensities. We used six functional traits (apical shoot relative growth rate (RGR), total shoot RGR, relative elongation, root length, lateral spread, branching degree) to measure the environmental response of the species. We calculated plasticity indexes to express the phenotypic differences between species.
Light and nitrogen jointly triggered the development of phenotypic characteristics that makes E. nuttallii a more successful invader in eutrophic waters than E. canadensis. The stronger invader showed a wider range of phenotypic plasticity. The apical elongation was the main difference between the two species with E. nuttallii being more than two times longer than that of E. canadensis. Elodea canadensis formed dense side shoots already at high shade and at low nitrogen levels, whereas E. nuttallii formed this at much higher light and nitrogen levels.
We found that under more eutrophic conditions E. nuttallii reach the water surface sooner than E. canadensis and by intensive branching outcompetes all other plants including E. canadensis. Our findings support the theory that more successful invaders have a wider range of phenotypic plasticity.