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Harvard Forest Symposium Abstract 2007

• Title: Effects of elevated CO2 on competitive dominance and genotypic composition in the invasive, allergenic plant, common ragweed.
• Primary Author: Kristina Stinson (University of Massachusetts - Amherst )
• Abstract:

  Invasive species may be successful outside their home ranges for a number of reasons, including increased competitive ability and genetic predisposition to invasiveness. Rising levels of atmospheric CO2 further compound the problem by potentially altering competitive dynamics that determine the size and abundance of populations, and perhaps by favouring a different suite of genotypes in future vs. current environments. Very little is known about the effects of CO2 on the genetic basis of competitive hierarchies, yet understanding this is critical for predicting the genetic composition and phenotypic properties of future plant populations. We investigated the effects of elevated CO2 on competitive interactions among dominant and subordinate genotypes of the allergenic plant, common ragweed (Ambrosia artemisiifolia L), a monoecious annual herb found growing wild and in abundance throughout most of North America that is rapidly becoming invasive across Europe. Twelve genotypes of ragweed from known maternal lines were selected and grown competitively in stands in open top chambers (OTC’s) at ambient (360 µL L-1) and elevated (720 µL L-1) CO2. There were six OTC’s and two stands within each OTC. Each genotype was replicated twice within each stand. Three OTC’s were maintained at ambient and three at elevated CO2 conditions during the experiment. Functional relationship models were developed to determine if catch-up occurred in common ragweed with respect to biomass and reproductive allocation. Model parameters were estimated using the NLMIXED procedure in SAS / STAT software Version 8.2 of the SAS System for Windows. We found novel evidence that those genotypes that perform less well under ambient CO2 conditions benefit proportionately more than other genotypes under elevated CO2, i.e., subordinate genotypes ‘catch-up’ to dominants. We found evidence of this phenomenon in both biomass and reproductive allocation under elevated CO2. The structure of populations changed under elevated CO2. Genotypes with a smaller biomass at ambient CO2 became the dominant genotypes under elevated (and vice versa). Genotypes with a smaller reproductive allocation at ambient CO2 were no longer subordinate under elevated CO2 as all genotypes tended to a common reproductive allocation. Thus, genotypes that are currently subordinate may become more dominant relative to their neighbours in future environments and more individuals are likely to contribute both pollen and seed to future populations. This is the first study to demonstrate a genetic basis for dominance hierarchies within developing stands, and to show how elevated CO2 can alter these hierarchies to affect future stand dynamics and genetic composition. Coupled with current predicted increases in ragweed pollen productivity under high CO¬2, the outlook for this species includes increased human health concerns as well as increased overall invasiveness.
  
  
  
  

• Research Category: Invasive Plants, Pests & Pathogens
  Physiological Ecology, Population Dynamics, and Species Interactions