Aimée T. Classen
Environmental Sciences Division
Oak Ridge National Laboratory
Oak Ridge, TN 37831-6422
classenat@ornl.gov
phone: 865-574-7848

Staff Scientist
Environmental Sciences Division
Oak Ridge National Laboratory

Research Assistant Professor
Ecology & Evolutionary Biology
University of Tennessee

 

Major Research Interests

Ecosystem ecology, global change, plant-herbivore interactions, microbial ecology, nutrient cycling, ecogenomics

Research in our group focuses on the interactions and feedbacks among communities of plants, herbivores, and microbes and ecosystem processes, especially carbon and nutrient cycling. We use a combination of experimental, field, laboratory, and modeling approaches to pursue three main questions: (1) How do climatic or anthropogenic driven changes in communities (plant, herbivore, microorganism) alter nutrient cycling? (2) How can single species and the genetic variation within a species alter ecosystem processes and trajectories? (3) What are the relationships among biodiversity and ecosystem resistance and resilience to natural and anthropogenic environmental perturbations such as climatic change?

Biogeochemical and microbial responses to natural and anthropogenic disturbances

One area of research focuses on biogeochemical responses to natural and anthropogenic disturbance such as global change, plant invasion, and herbivore outbreaks. For example, we are collaborating with Richard Norby (ORNL) and Jake Weltzin (UT) investigating how elevated atmospheric carbon dioxide, warming, water availability, and plant species composition alter decomposition and nutrient cycling in a constructed Tennessee old field ecosystem (known as the Old Field Community Climate and Atmospheric Manipulation or OCCAM project). Plots containing seven different grassland species (a mix of C3 grasses, C4 grasses, and legumes) are exposed to either ambient or elevated atmospheric carbon dioxide combined with ambient or elevated air temperature. Each chamber is split with two levels of soil moisture (http://warming.ornl.gov/OCCAM.html).

Community and species effects on ecosystem properties

We are also interested in understanding how a single species, or the genetic variation within a species, can impact both community structure and ecosystem function. For example, ongoing research in our lab investigates how chronic insect infestation of piñon pine by a needle scale or stem-boring moth alters the nitrogen and carbon budget of a piñon-juniper woodland and how these herbivores indirectly alter litter and soil microbial community diversity and function. Long-term studies in northern Arizona have identified trees that are resistant and susceptible to each herbivore, and because piñon resistance to herbivory has a genetic component, the potential exists for linking population-level variation in plant genetics to key ecosystem processes. We collaborate on this project with Tom Whitham (NAU) , Steve Hart (NAU) , George Koch (NAU) , and Samantha Chapman (SERC) (http://www.mpcer.nau.edu/ug/perg.html).

In another project we are collaborating with Aaron Ellison (Harvard Forest) and Nathan Sanders (UT) to investigate the direct and indirect effects of Hemlock Woolly Adelgid on soil processes and nutrient dynamics, and how these effects are mediated by ants. We are in the process of establishing plots and collecting preliminary data at Harvard Forest in MA and Coweeta Hydrologic Laboratory in NC.

Linking genes to ecosystem function

We are also interested in testing the prediction that information expressed at the genomic and metabolic levels for evolutionarily conserved and ubiquitous genes is sufficient for estimating the ecosystem function to which such genes are coupled. For example, separation of soil respiration into component fluxes is an important research priority, but no extant techniques can unambiguously separate plant from microbial respiration. In collaboration with Chris Schadt (ORNL), Hector Castro Gonzalez (ORNL), and Richard Norby we are using genetic techniques to try and separate plant and microbial soil respiration. We hypothesize that processes measured at the level of gene transcripts will be predictive of organismal respiration, which in turn can be used to estimate ecosystem-scale respiration.

Student projects in the laboratory

Colleen Iversen is a PhD candidate and DOE GREF fellow at UT who collaborates with us on the ORNL FACE (Free Air CO2 Enrichment) project. Colleen's work aims to quantify the importance of climate driven changes in fine root morphology and chemistry on belowground processes, such as carbon and nutrient cycling. New insight gained from Colleen's research will be valuable in extrapolating key belowground processes within and among ecosystems.

Greg Crutsinger is a PhD candidate in the Sanders Lab at UT. Greg's work explores the links between genes, ecological communities, and ecosystems by examining the relationship between population genetic diversity in host plants, the structure of associated arthropod communities, and ecosystem processes.

Katherine Sides is a post-BA working with our group on both the FACE and OCCAM projects. Katherine assists us with all aspects on both these projects, but her interests lie belowground with a focus on soil respiration and the factors that drive changes in respiration. Katherine joined the lab in the summer of 2005.

Emmi Feckler-Quinn recently graduated from Smith College and is our new post-BA field technician. Emmi is interested in invasion biology and the effect of climatic change on plant communities.

Sharon Gray will graduate from University of Illinois at Urbana-Champaign this January and is working in the lab as a DOE SURE fellow this summer. Sharon is interested in ecogenomics and is working on the soil respiration project with Hector Castro.

Luke Zachmann graduated from the University of Minnesota, Morris this spring and is working int he lab this summer as a DOE SURE fellow. Luke is interested in exploring the relationships between biodiversity and ecosystem resistance and resilience to natural and anthropogenic environmental perturbations such as climate change. Luke is working with Greg Crutsinger on his goldenrod project examining decomposition and soil respiration.

Rebecca Roha is an undergraduate student at Gettysburg College. Rebecca is working on a decomposition and nutrient cycling project at ORNL FACE. Rebecca joined our lab for the summer of 2006.

Marlene Tyner is an undergraduate student at the University of Michigan. Marlene is a SULI student working on a project examining decomposition and nutrient cycling in the OCCAM project. Marlene joined the lab for the summer of 2006.

Emily Mitchell graduated from Oak Ridge High School this spring and will be attending Austin Peay State University in the fall. Emily is interested in education and has been working on a variety of projects this summer- including FACE, OCCAM, and the goldenrod project.

Ecosystem Lab Alumni

Kerri Crawford graduated from UT in 2006 and is interested in exploring the links between plant genetics and herbivore populations on Solidago. Kerri is collaborating with us to set up several decomposition studies examining how shifts in genetic structure of plant populations will affect decomposer communities, decomposition, and nutrient dynamics in an old-field ecosystem. This summer, Kerri is working with Hector Castro on the soil respiration genomics project. Kerri joined the lab during the winter of 2006 and will be starting a PHD program at Rice University this fall.

Katrina Cox is an undergraduate at Rhone State who assists us with the FACE and OCCAM projects. Katrina joined the lab in the summer of 2005 and worked with us until May 2006. In addition to helping us maintain the lab, Katrina assisted with many field and laboratory projects.

Sam Freyladenhoven is an undergraduate at Hendrix College who assisted us with the FACE and OCCAM projects. Sam worked with our group from June - August 2006.

Other research in the laboratory

We are involved with field experiments and modeling efforts at the ORNL FACE site (Free Air CO2 Enrichment). We are interested in predicting and measuring the effects of elevated atmospheric carbon dioxide on decomposition and belowground processes such as root production and proliferation and gross nitrogen mineralization (http://www.esd.ornl.gov/facilities/ORNL-FACE/index.html).

We are also interested in questions involving the ecotonal boundaries between terrestrial and aquatic ecosystems. We are pursuing some of these ideas with Carri Le Roy (Evergreen State), Jennifer Schweitzer (NAU & UT), and Brian Roberts (ORNL).

Selected Publications

Modified August 1, 2006