The Effects of Ozone Pollution on the Foliar Chemical Landscape of a Tropical Broadleaf Forest

EPA Grant Number: F13F31245
Title: The Effects of Ozone Pollution on the Foliar Chemical Landscape of a Tropical Broadleaf Forest
Investigators: Schneider, Gerald Franklin
Institution: University of Utah
EPA Project Officer: Lee, Sonja
Project Period: August 25, 2014 through August 25, 2016
Project Amount: $84,000
RFA: STAR Graduate Fellowships (2013) RFA Text |  Recipients Lists
Research Category: Academic Fellowships , Fellowship - Ecology

Objective:

Do current levels of ozone pollution in an urban-influenced tropical forest cause qualitative and/or quantitative changes in the chemical defenses of the trees therein? If so, are certain plant species and certain types of chemicals more affected than others? Finally, are herbivory rates affected by these changes in defense chemistry?

Approach:

This project will focus on the tropical forest at Barro Colorado Island, Panama, which shares an airshed with two large sources of ozone precursor emissions: the Panama Canal and Panama City. Ozone concentrations exhibit a marked decrease from the forest canopy and edges toward the forest interior, and the extremes of this gradient will be used as the spatial points of comparison for this study. Potted saplings of five tree species common in this forest will be placed at both extremes of the ozone gradient, with shade cloth used where applicable to standardize the light environment. The saplings will be left in place for two iterations of leaf production. During this time, ozone concentrations, stomatal aperture, emissions of volatile defense chemicals and herbivory levels will be monitored regularly. All leaves will then be harvested and their defense chemistry analyzed using liquid chromatography and mass spectrometry.

Expected Results:

If current levels of ozone pollution at Barro Colorado Island are sufficient to induce changes in leaf chemical defenses, these changes will most likely come in the form of increased production of phenolic compounds and possibly terpenoid compounds. While many phenolic and terpenoid compounds function as anti-herbivore defenses, others appear to function in mitigating oxidative stress. An evaluation of chemical changes in the context of herbivory levels is necessary to determine which functional types of phenolics and terpenoids are regulated in response to ozone. These responses will likely be species specific, considering the high chemical diversity within tropical tree communities. For example, antioxidant phenolics and terpenoids may be upregulated while anti-herbivore compounds exhibit no change in concentration or are downregulated, resulting in increased herbivory rates. Alternatively, some species’ anti-herbivore compounds also may function as antioxidants, and these will likely be upregulated, resulting in decreased herbivory rates. Finally, many tropical tree species exhibit delayed greening of expanding leaves and, thus, have minimal stomatal activity during the period when they are most vulnerable to herbivory and most heavily defended by antiherbivore chemicals. These species will likely be much less affected by ozone than those species that initiate photosynthesis while leaves are still expanding.

Potential to Further Environmental/Human Health Protection

In tropical and temperate zones alike, trees are crucial elements of forest food webs, as well as of ecosystem services provided to society by forests. Because trees’ interactions with pests are chemically mediated, changes in plant chemicals due to pollution could have extensive and long-term effects on ecosystems and ecosystem services. This study will explore the chemical responses of trees in a tropical forest to ground-level ozone, a globally increasing form of air pollution.

Supplemental Keywords:

ozone, plant defense chemistry, plant physiology

Progress and Final Reports:

  • 2015
  • Final