Recent CO2 levels promote increased production of the toxin parthenin in an invasive Parthenium hysterophorus biotype

Recent carbon dioxide (CO2) concentrations promoted higher parthenin concentrations in an invasive Parthenium hysterophorus biotype. Mean concentrations of parthenin, an allelopathic and defensive sesquiterpene lactone, were 49% higher at recent (~400 ppm) than at mid-twentieth-century (~300 ppm) CO2 concentrations, but did not vary in a non-invasive biotype, suggesting that recent increases in atmospheric CO2 may have already altered the chemistry of this destructive weed, potentially contributing to its invasive success. Not only is climate change having an impact on invasive plants through changes in ecosystem, atmospheric carbon may be changing the plants themselves. This analysis finds higher concentrations of parthenin at higher levels of CO2, making an invasive weed more toxic.