Light Competition in Elevated CO2 Environments: Does CO2 Enrichment Help Canopy Subordinates 'Catch Up'?

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Competition for light in plant stands causes size differences to develop among plants, even if they are of the same age and species. However, preliminary research from the investigator's lab suggests that, under elevated CO2 environments (predicted to occur in the future), these size differences might be reduced. Because larger plants often also produce more seed, the development of these size hierarchies affects which individuals successfully reproduce. Thus, if there is any genetic influence on which plants become dominant, the effect of elevated CO2 on size structures in stands may also affect genetic or evolutionary change in a species.The goals of this research are to determine the physiological, architectural and genetic bases for size hierarchy development, and to test whether elevated CO2 will help low-light subordinates "catch up". To answer these questions, experimental populations of Ambrosia artemisiifolia will be grown in open-top chambers at two atmospheric CO2 concentrations over two growing seasons. Effects of elevated CO2 on light interception, leaf physiology, architecture, and reproductive output will be measured and modeled (1) to elucidate the dynamics of light competition and the development of size and fitness hierarchies in plant populations, and (2) to determine if elevated CO2 will reduce the importance of light competition in determining the relative fitness of individuals in future environments. In addition, because the study species (ragweed) is one of agronomic and public health concern, information from this study on its changing biology may have management implications.