What was done
Is the competitive dominance of exotic invasive plant species exacerbated by an increase in the air's CO2 content, as certain people would like to have us believe? In an effort to answer this question, the authors grew model communities containing six herbaceous C3 plant species typical of riparian communities in the United Kingdom (Calystegia sepium, Epilobium hirsutum, Poa trivialis, Ranunculus repens, Rumex obstusifolius and Urtica dioica) either in competition with each other or in competition with three exotic invasive herbaceous C3 plant species (Fallopia japonica, Impatiens glandulifera and Mimulus guttatus) within controlled-environment chambers maintained at either 375 or 750 ppm CO2 for two 70-day growing periods, between which there was a simulated "winter" of 56 days duration, after which plant biomass assessments were conducted.

What was learned
Bradford et al. confirmed that the invasive species were indeed better competitors than the native species. However, they found that the elevated CO2 treatment "did not modify the effects of the invasive species on [the] native plant assemblages." In fact, as best we can determine from the bar graphs of their results, the native plants experienced a mean CO2-induced biomass increase of 25% when grown by themselves, but a 33% increase when grown in competition with the invasive plants.

What it means
The international team of scientists (from the US, UK and Germany) concluded that although their results "confirm the expectation that invasive species alter the characteristics of native assemblages," their findings led them to question the hypothesis that elevated resource availability, such as that provided by atmospheric CO2 enrichment, will magnify these effects. It is the inference of this particular study, therefore, that the decimation of natural plant communities throughout the world by more competitive invasive species from far-flung regions of the globe is not exacerbated by the ongoing rise in the air's CO2 content.