Highly plastic response in morphological and physiological traits to light, soil-N and moisture in the model invasive plant, Phalaris arundinacea

The ability of an introduced species to thrive is often influenced by its capacity to cope with disturbance and resource fluctuation, and one way to cope is by being phenotypically plastic. The biomass and resource allocation of the invasive plant species, Phalaris arundinacea (reed canarygrass), to contrasting levels of light, soil-N and moisture was evaluated. We predicted that P. arundinacea would show a highly plastic response in important growth and physiological traits to treatment conditions (presence of three-way interactions and large phenotypic plasticity index (PI) values) because of its ability to persist in variable environments. MANOVA tests showed significant three-way interactions for each of the three groups of plant traits (aboveground (AGB) and belowground biomass (BGB), shoot C/N and root C/N ratios, leaf chlorophyll and soluble protein), demonstrating the complex correlated response to the treatment effects by pairs of response variables. There were significant three-way interactions for seven of nine plant traits (univariate analyses), including AGB and BGB, AGB per tiller, shoot/root ratio, shoot C/N ratio, root C/N ratio and leaf chlorophyll content. Total plasticity values, which represented the greatest possible plasticity for each plant trait, were larger than any of the PI values for the main effects. Understanding which traits show plasticity, as well as the magnitude of response expressed in common invasive species is an important area of research because aspects of their aggressive behavior may be explained by how they grow and allocate resources under variable environmental conditions, which in turn can be important when seeking to make predictions about the probability and degree of invasion success with species-specific invasion models.

► Phalaris arundinacea had the greatest plasticity in response to light.
► Effects of moisture and nitrogen on biomass were magnified at the high light level.
► Biomass increased with increasing moisture at high nitrogen level.
► Tiller production was greatest in high light conditions.
► Shoot C/N ratio varied less than root C/N ratio in high light, low nitrogen conditions.