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Northern Research Station
One Gifford Pinchot Drive
Madison, WI 53726
(608) 231-9318
(608) 231-9544 TTY/TDD

Clean Air and Water

Tracing Carbon Flux and Stabilization Using Ecosystem-scale Radiocarbon Enrichment

Research Issue

Most carbon in forests is not in the trees, but is actually in the soil.  If we ultimately seek to predict how carbon will cycle through the forest ecosystem, we first need to understand how carbon cycles through the soil.  Questions of interest are then: how does carbon enter the soil, how is it stabilized, and how is it released?

[photo:] Field plot (7m x 7m) of the reciprocal litter transplantOur Research

The Enriched Background Isotope Study, led by Paul Hansen of Oak Ridge National Laboratory and primarily supported by the DOE Office of Science (Terrestrial Carbon Processes), takes advantage of an extraordinary opportunity: tracing a large atmospheric pulse of enriched radiocarbon (14C) through an entire forest ecosystem on the Oak Ridge Reservation in eastern Tennessee.  During the summer of 1999, emissions from a local incinerator added a large pulse of 14CO2 to the local atmosphere, which was subsequently fixed by photosynthesizing vegetation and incorporated into leaves, stems, and roots.  Fallen leaves were collected from 14C-enriched and near-background areas of the forest in the fall of 2000.  These litter sources were deployed in a reciprocal litter transplant experiment.  Highly enriched leaves were placed in background-14C stands for three consecutive years, while background-14C leaves were placed in highly enriched stands.  The combination of local 14C gradients and litter manipulations has allowed us to trace the flux of enriched 14C from known sources (leaves, roots) through various soil carbon pools, giving us insights into the sources, movement, and stabilization of soil carbon.

Expected Outcomes

Radiocarbon flux through these soils has been characterized using numerous approaches, including measurement of radiocarbon in bulk organic and mineral soils, dissolved and particulate organic matter, microbial biomass, organo-mineral complexes, and soil gas.  A common theme has emerged from the results of each of these approaches: recent inputs to the mineral soil carbon cycle appear to be dominated by root litter, whereas canopy litter contributes to a largely independent surface carbon cycle.  We are currently pursuing subsequent tests of this idea at several other ecosystems.

Research Results

Fröberg, M., P.M. Jardine, P.J. Hanson, C.W. Swanston, D.E. Todd, J.R. Tarver, and C.T. Garten Jr. 2007. Low dissolved organic carbon input from fresh litter to deep mineral soils. Soil Science Society of America Journal 71:347-354.

Cisneros-Dozal, L.M., S. Trumbore, and P.J. Hanson. 2006. Partitioning sources of soil-respired CO2 and their seasonal variation using a unique radiocarbon tracer. Global Change Biology 12:194-204.

Joslin, J.D., J.B. Gaudinski, M.S. Torn, W.J. Riley, and P.J. Hanson. 2006. Fine-root turnover patterns and their relationship to root diameter and soil depth in a 14C-labeled hardwood forest. New Phytologist 172:523-535.

Treseder, K.K., M.S. Torn, and C.A. Masiello. 2006. An ecosystem-scale radiocarbon tracer to test use of litter carbon by ectomycorrhizal fungi. Soil Biology and Biochemistry 38:1077-1082.

Swanston, C.W., M.S. Torn, P.J. Hanson, J.R. Southon, C.T. Garten, E.M. Hanlon, and L. Ganio. 2005. Initial characterization of processes of soil carbon stabilization using forest stand-level radiocarbon enrichment. Geoderma 128:52-62.

Hanson, P.J., C.W. Swanston, C.T. Garten Jr., D.E. Todd, and S.E. Trumbore. 2005. Reconciling change in Oi-horizon carbon-14 with mass loss for an oak forest. Soil Science Society of America Journal 69:1492-1502.

For more information including a project abstract, related publications, summaries, and presentations, photographs, maps and diagrams, and a list of participants, please visit:

Research Participants

  • Paul Hanson (Lead PI), Oak Ridge National Lab
  • Sue Trumbore, University of California, Irvine
  • Chris Swanston, US Forest Service, NRS
  • Margaret Torn, Lawrence Berkeley National Lab
  • Julie Jastrow, Argonne National Lab
  • Mac Callaham, US Forest Service, SRS
  • Christiane Kramer, University of California, Irvine
  • William J. Parton Jr., Colorado State University, NREL
  • Roser Matamala, Argonne National Lab
  • Tom Guilderson, Lawrence Livermore National Lab
  • Karis McFarlane, Lawrence Livermore National Lab

Last Modified: 01/28/2009

Featured Product

Fröberg, M., P.M. Jardine, P.J. Hanson, C.W. Swanston, D.E. Todd, J.R. Tarver, and C.T. Garten Jr. 2007. Low dissolved organic carbon input from fresh litter to deep mineral soils. Soil Science Society of America Journal 71:347-354.