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Aimée T. Classen

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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 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 Rich Norby (Oak Ridge National Lab) and Jake Weltzin (University of TN) investigating how elevated CO2, 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 CO2 combined with ambient or elevated 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, previous research in our lab involved investigating 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, Steve Hart, George Koch, and Sam Chapman at Northern Arizona University (http://www.mpcer.nau.edu/ug/perg.html).

In another project we are collaborating with Aaron Ellison (Harvard Forest) and Nate Sanders (University of Tennessee) 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 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, Hector Castro, and Rich Norby (ORNL) we are using genetic techniques to try and separate plant bacterial, and fungal respiration from bulk 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.

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.

We are also interested in questions involving the ecotonal boundaries between terrestrial and aquatic ecosystems.

Education

  • 2004 - Ph.D., Northern Arizona University

Selected Publications

  • Garten CT, Classen AT, Norby RJ, Brice DJ, Weltzin JA, and Souza L (2008) Role of N2-fixation in constructed old-field communities under different regimes of [CO2], temperature, and water availability. Ecosystems 11: 125-137.
  • Crutsinger GM,  Habenicht MN, Classen AT, Schweitzer JA, and Sanders NJ (2008) Galling by Rhopalomyia solidaginis alters Solidago altissima architecture and litter nutrient dynamics in an old-field ecosystem. Plant and Soil 303:95-103.
  • Classen AT, Chapman SK, Whitham TG, Hart SC, and Koch GW (2007) Genetic-based plant resistance and susceptibility traits to herbivory influence needle and root litter nutrient dynamics. Journal of Ecology 95:1181-1194.
  • Classen AT, Overby ST, Hart SC, Koch GW, and Whitham TG (2007) Season mediates herbivore effects on litter and soil microbial abundance and activity in a semi-arid woodland. Plant and Soil 295:217-227.
  • Classen AT, DeMarco J, Hart SC, Whitham TG, Cobb NS, and Koch GW (2006) Impacts of herbivorous insects on decomposer communities during the early stages of primary succession in a semi-arid woodland. Soil Biology & Biochemistry 38:972-982.
  • Classen AT, Hart SC, Whitham TG, Cobb NS, and Koch GW (2005) Insect infestations linked to shifts in microclimate: important climate change implications. Soil Science Society of America Journal 69:2049-2057.
  • Hart SC, Classen AT, and Wright RJ (2005) Long-term interval burning alters fine root and mycorrhizal dynamics in a ponderosa pine forest. Journal of Applied Ecology 42:752-761.
Aimée T. Classen

Contact Information

Aimée T. Classen
Research Assistant Professor
Ecology and Evolutionary Biology
Staff Scientist, Environmental Sciences Division, Oak Ridge National Laboratory
569 Dabney Hall
University of Tennessee
Knoxville, TN 37996-1610

Phone: (865) 974-7848
Fax: (865) 974-9939
Email: aclassen@utk.edu