Differences in phenotypic plasticity between native and invasive plants mediated by rhizobia

Background/Question/Methods

Phenotypic plasticity can contribute to the success of invasive plants. Invasiveness may be especially likely when plants can change their phenotype in response to the environment when establishing in novel habitats. This plasticity could also contribute to the competitive superiority of invaders under fluctuating environmental conditions. Previous studies have shown that invaders tend to be more plastic than natives, and that this plasticity sometimes leads to a fitness benefit, which suggests plasticity can play a role in invasion success. Many plasticity studies comparing native and invasive species focus on plasticity in response to abiotic factors. However,  biotic factors, such as plant-associated microbes, can potentially influence plant phenotypic plasticity. Yet during invasions, colonizing propagules are thought to often leave behind their native microbial communities, which could have implications for invader plasticity.  In a study manipulating light, nitrogen, and nitrogen-fixing rhizobia availability, I examined trait plasticity of native and invasive legume species to determine whether native and invasive species differ in plasticity, and whether differences in plasticity were mediated by rhizobia.

Results/Conclusions

Invasive species showed greater plasticity than natives for some traits, but not others. These plasticity differences were often mediated by rhizobia. Invader height and biomass were more plastic in response to nitrogen, but only in the absence of rhizobia. Invader biomass was also more plastic in response to light, but only in the presence of rhizobia, while native root:shoot biomass ratio was more plastic under the same conditions. Native root nodule weight and specific leaf area were more plastic in response to nitrogen and light, respectively, regardless of rhizobia treatment. I am currently exploring the relationship between plasticity in these traits and estimated fitness. Given that invasive and native species both show higher plasticity for some traits, the results of this study do not suggest that plasticity plays a large role in invasion success. However, the results do indicate that rhizobia play a role in mediating plasticity, and suggest that plant-microbial associations should be taken into account in studies of phenotypic plasticity.