Southern Piedmont grassland community structure and functioning under future climate scenarios of elevated tropospheric ozone and altered rainfall amounts.

Art Chappelka, Professor

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The physical and chemical climate of the earth has changed rapidly over the last 100 years and is predicted to change dramatically in the future. Models predict that tropospheric ozone (O3) concentrations will increase on a global basis for the next 50 yrs while summer rainfall may either decrease or increase ~10–20% based on model predictions in the Southeastern United States. This region is experiencing rapid population growth and includes a number of areas in noncompliance with current NAAQS for O3. Increases in O3 in combination with altered rainfall amounts have been little studied in grassland ecosystems in the Southern Piedmont region which covers 17 million ha from central Virginia into eastern Alabama. The study area is approximately 5 km from Auburn University and contains open-top chambers (OTCs), equipment and monitoring sheds, office and laboratory facilities. To establish a typical managed grassland community, 12 OTCs were seeded (March 2007) with a mixture of tall fescue (Festuca arundinacea, C3, cool-season grass), common bermudagrass (Cynodon dactylon, C4 warm-season grass), dallisgrass (Paspalum dilatatum C4, warm-season grass) and ladino clover (Trifolium repens, C3 cool-season legume). Our (Art Chappelka, SFWS and Russ Muntifering, Dept. of Animal Science, Investigators) global hypothesis is that exposure to elevated O3 alone or in combination with altered rainfall amounts modifies resource acquisition and biomass allocation of dominant, managed-grassland species in such a way that community structure and functioning of the system is impacted. Specific hypotheses include: 1) Species with higher stomatal conductance (gs) will be more adversely affected by elevated O3 than those with lower gs because uptake (and hence dose) will be greater, resulting in shifts in productivity and species composition and productivity over time; 2) The effects of O3 and altered rainfall amounts will be mediated by changes in gs and canopy-level responses such as changes in cover and structure; and 3) Elevated O3 will increase production of plant secondary metabolites, notably lignin, and these shifts in energy allocation will be altered by either decreased or increased rainfall additions. Various field measurements (species abundance, richness, gas exchange and water relations,) and laboratory methodologies (plant defensive compounds, chlorophyll analysis) will be used to test the specific hypotheses. Integration of various measures of diversity and productivity and underlying physiological and biochemical responses will enable a more complete characterization and modeling of potential impacts of future climate change scenarios on these plant communities. Funding is provided through USDA Hatch funds. A graduate student: Nick Gilliland (MS) is conducting research on different aspects of this project.