New Harvard Forest Publication: Ragweed Genotypes and Climate Change

Harvard Forest scientist Kristina Stinson and colleagues from University College, Dublin, Ireland, published a new paper in Ecosphere predicting changes in the genetic composition of common ragweed populations under global change conditions. Common ragweed, or Ambrosia artemisiifolia, produces pollen that is a leading cause of fall hay fever allergies. In experimentally elevated CO2 conditions, this plant can produce 60% more pollen than it does in present day conditions. The researchers tested how projected changes in CO2 levels might preferentially increase the growth and reproduction of certain genotypes over others. They grew twelve genotypes in experimental stands, at either ambient or twice-ambient levels of CO2, and modeled the relative performance of genotypes in the two treatments. One surprising result from the study is that genotypes that remain small in today's environment become large under experimental doubling of CO2, while normally larger plants become suppressed. Smaller plants, in turn, boost their reproductive allocation to match that of large plants, shrinking the fitness gap among all genotypes in high CO2. As a result, natural selection on size is reduced at elevated CO2, because an individual's relative position within the size hierarchy becomes less important for reproduction than it is in ambient conditions. This work points broadly to unknown evolutionary changes in future plant populations, as well as to potential changes in the ecological and human-health impacts of this widespread allergenic plant.

Stinson, K.A., C. Brophy and J. Connoll. 2011. Catching up on global change: new ragweed genotypes emerge in elevated CO2 conditions, Volume 2(4)