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Nutrient additions to a tropical rain forest drive substantial soil carbon dioxide losses to the atmosphere

  1. Cory C. Cleveland * , † and
  2. Alan R. Townsend * , ‡
  1. *Institute of Arctic and Alpine Research, Campus Box 450, and
  2. ‡Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO 80309

  1. Edited by Peter Vitousek, Stanford University, Stanford, CA, and approved May 20, 2006 (received for review February 6, 2006)

Abstract

Terrestrial biosphere–atmosphere carbon dioxide (CO2) exchange is dominated by tropical forests, where photosynthetic carbon (C) uptake is thought to be phosphorus (P)-limited. In P-poor tropical forests, P may also limit organic matter decomposition and soil C losses. We conducted a field-fertilization experiment to show that P fertilization stimulates soil respiration in a lowland tropical rain forest in Costa Rica. In the early wet season, when soluble organic matter inputs to soil are high, P fertilization drove large increases in soil respiration. Although the P-stimulated increase in soil respiration was largely confined to the dry-to-wet season transition, the seasonal increase was sufficient to drive an 18% annual increase in CO2 efflux from the P-fertilized plots. Nitrogen (N) fertilization caused similar responses, and the net increases in soil respiration in response to the additions of N and P approached annual soil C fluxes in mid-latitude forests. Human activities are altering natural patterns of tropical soil N and P availability by land conversion and enhanced atmospheric deposition. Although our data suggest that the mechanisms driving the observed respiratory responses to increased N and P may be different, the large CO2 losses stimulated by N and P fertilization suggest that knowledge of such patterns and their effects on soil CO2 efflux is critical for understanding the role of tropical forests in a rapidly changing global C cycle.

Footnotes

  • †To whom correspondence should be addressed. E-mail: cory.cleveland{at}colorado.edu

  • Author contributions: C.C.C. and A.R.T. designed research, performed research, analyzed data, and wrote the paper.

  • Conflict of interest statement: No conflicts declared.

  • This paper was submitted directly (Track II) to the PNAS office.

  • Abbreviations:

    Abbreviations:

    ha,
    hectare;
    NPP,
    net primary production.

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