Letters to Nature

Nature 388, 576-579 (7 August 1997) | ; Received 10 January 1997; Accepted 9 June 1997

The fate of carbon in grasslands under carbon dioxide enrichment

Bruce A. Hungate1,2, Elisabeth A. Holland3, Robert B. Jackson4, F. Stuart Chapin, III1, Harold A. Mooney5 and Christopher B. Field6

  1. Department of Integrative Biology, University of California, Berkeley, California 94720, USA
  2. Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, Colorado 80307, USA
  3. Department of Biological Sciences, Stanford University, Stanford, California 94305, USA
  4. Department of Botany, University of Texas at Austin, Austin, Texas 78713, USA
  5. Carnegie Institution of Washington, Department of Plant Biology, Stanford, California 94305, USA
  6. Present address: Smithsonian Environmental Research Center, Edgewater, Maryland 21037, USA.

Correspondence to: Bruce A. Hungate1,2 Correspondence and requests for materials should be addressed to B.A.H. (e-mail: Email: hungate@serc.si.edu).

The concentration of carbon dioxide (CO2) in the Earth's atmosphere is rising rapidly1, with the potential to alter many ecosystem processes. Elevated CO2 often stimulates photosynthesis2, creating the possibility that the terrestrial biosphere will sequester carbon in response to rising atmospheric CO2 concentration, partly offsetting emissions from fossil-fuel combustion, cement manufacture, and deforestation3,4. However, the responses of intact ecosystems to elevated CO2 concentration, particularly the below-ground responses, are not well understood. Here we present an annual budget focusing on below-ground carbon cycling for two grassland ecosystems exposed to elevated CO2 concentrations. Three years of experimental CO2 doubling increased ecosystem carbon uptake, but greatly increased carbon partitioning to rapidly cycling carbon pools below ground. This provides an explanation for the imbalance observed in numerous CO2 experiments, where the carbon increment from increased photosynthesis is greater than the increments in ecosystem carbon stocks. The shift in ecosystem carbon partitioning suggests that elevated CO2 concentration causes a greater increase in carbon cycling than in carbon storage in grasslands.