Judges’ Queries and Presenter’s Replies

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Presentation Discussion

  • Icon for: David Toledo

    David Toledo

    May 23, 2012 | 12:03 p.m.

    Hi Douglas, Interesting work. I have a couple questions. Does your research take into account depositions of particulates on leaf surfaces that might create a physical barrier to light or nutrients? Also, how do you decide if what you are seeing is due to air pollution or if it is due to some other stressor?

  • Icon for: Douglas Lynch

    Douglas Lynch

    May 23, 2012 | 02:04 p.m.

    Hi David, thanks for your interest. For your 1st question, if particulate deposition rate were significant enough to reduce the leaf’s ability to capture light and plant-level photosynthesis was reduced, this would be reflected in the isotopic composition. To my knowledge, there isn’t evidence that this has been the case, especially as a rain event washes off most of the deposition- which in my sites is very regular.
    For your second question, assigning changes in growth rate to a particular stressor is challenging. That’s why I think a multi-variable approach is very useful. N isotopes and concentrations can provide a record of N deposition, sulfur concentrations provide a record of sulfur deposition, and base cation concentrations can provide a record of soil pH (which can impact plant nutrition). I’ll include precipitation and temperature records in my analysis (which are main drivers for short-term growth). A statistical model that includes at least a majority of the possible variables driving changes in plant growth should give pretty good confidence about what is most affecting the tree.

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Icon for: Douglas Lynch


University of Illinois at Chicago
Years in Grad School: 3

Impacts of long-term air pollution on trees through analysis of tree ring chemistry

Human activities release atmospheric pollutants that can impact tree growth and health. Some changes in the atmosphere have positive impacts on plants including carbon dioxide and nitrogen deposition. Other atmospheric pollutants have negative impacts on plants including sulfur dioxide and ozone. The total net effects from air pollution in natural ecosystems are not well understood. Improving understanding of these effects is important, both for management of natural areas and in quantifying the impacts of human activity on natural ecosystems. Trees in temperate regions have distinct annual growth patterns that allow for the measurement of physical properties of wood from each year of growth. Of particular use are long-lived trees that can provide a long-term record of environmental conditions experienced by the tree. This study will analyze chemical properties of tree rings from Quercus spp. in the Chicago, Illinois region to provide a record of environmental conditions from pre-industrial times through the present. In particular, the carbon isotope composition of wood is useful as a proxy for exposure to environmental stress. Several recent studies have demonstrated changes in tree-ring carbon isotopic composition with exposure to industrial pollutants. We will analyze changes in isotopic composition in trees proximate to an urban region where trees have experienced long-term exposure to high concentrations of atmospheric pollutants. Results will demonstrate the effects of industrial pollutants on tree physiology and document recovery from environmental stressors with the reduction of emissions in recent decades due to environmental legislation, as has been shown in other ecosystems.