I tested whether elevated [CO2] affected which genotypes of Taraxacum officinale had highest fitness in two field experiments. In one experiment, T. officinale plants which persisted as weeds in alfalfa plots in open top chambers at ambient and elevated [CO2] were compared. In a second experiment, T. officinale seeds collected from local habitats were mixed and scattered in open top chambers at ambient and elevated [CO2], and plants producing seeds after one and two years in monocultures were compared. In both experiments seeds produced in each chamber were collected, and many plants from the seed lot from each chamber were grown in controlled environment chambers to test whether the [CO2] of the chamber of origin affected the mean value of various plant parameters. In both experiments, the results indicated that field exposure to elevated [CO2] altered the relative fitness of genotypes. Elevated [CO2] favored genotypes which produced biomass more rapidly at elevated [CO2] in both experiments, primarily because of faster rates of leaf initiation. The results suggest that genotypes of this species vary widely in fitness at elevated [CO2] whether grown in monocultures or in mixed communities, and that this species could adapt rapidly to rising atmospheric [CO2].
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