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Letters to Nature

Nature 409, 188-191 (11 January 2001) | doi:10.1038/35051576; Received 18 October 2000; Accepted 3 November 2000

Nitrogen limitation of microbial decomposition in a grassland under elevated CO2

S. Hu1,2, F. S. Chapin, III1,2, M. K. Firestone3, C. B. Field4 & N. R. Chiariello4

  1. Department of Integrative Biology, University of California, Berkeley, California 94720, USA
  2. Department of Environmental Science, Policy and Management, University of California, Berkeley, California 94720, USA
  3. Carnegie Institution of Washington, Department of Plant Biology, Stanford, California 94305, USA
  4. Present address: Department of Plant Pathology, North Carolina State University, Raleigh, North Carolina 27695, USA (S.H.); Institute of Arctic Biology, University of Alaska, Fairbanks, Alaska 99775, USA (F.S.C.).

Correspondence to: Correspondence and requests for materials should be addressed to S.H. (e-mail: Email: shuijin_hu@ncsu.edu).

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Carbon accumulation in the terrestrial biosphere could partially offset the effects of anthropogenic CO2 emissions on atmospheric CO 2 (refs 1, 2). The net impact of increased CO2 on the carbon balance of terrestrial ecosystems is unclear, however, because elevated CO2 effects on carbon input to soils and plant use of water and nutrients often have contrasting effects on microbial processes3, 4, 5. Here we show suppression of microbial decomposition in an annual grassland after continuous exposure to increased CO2 for five growing seasons. The increased CO 2 enhanced plant nitrogen uptake, microbial biomass carbon, and available carbon for microbes. But it reduced available soil nitrogen, exacerbated nitrogen constraints on microbes, and reduced microbial respiration per unit biomass. These results indicate that increased CO2 can alter the interaction between plants and microbes in favour of plant utilization of nitrogen, thereby slowing microbial decomposition and increasing ecosystem carbon accumulation.