The nitrogen paradox in tropical forest ecosystems

Lars O. Hedin, E. N.Jack Brookshire, Duncan N.L. Menge, Alexander R. Barron

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372 Scopus citations


Observations of the tropical nitrogen (N) cycle over the past half century indicate that intact tropical forests tend to accumulate and recycle large quantities of N relative to temperate forests, as evidenced by plant and soil N to phosphorus (P) ratios, by P limitation of plant growth in some tropical forests, by an abundance of N-fixing plants, and by sustained export of bioavailable N at the ecosystem scale. However, this apparent up-regulation of the ecosystem N cycle introduces a biogeochemical paradox when considered from the perspective of physiology and evolution of individual plants: The putative source for tropical N richness-symbiotic N fixation-should, in theory, be physiologically down-regulated as internal pools of bioavailable N build. We review the evidence for tropical N richness and evaluate several hypotheses that may explain its emergence and maintenance. We propose a leaky nitrostat model that is capable of resolving the paradox at scales of both ecosystems and individual N-fixing organisms.

Original languageEnglish (US)
Pages (from-to)613-635
Number of pages23
JournalAnnual Review of Ecology, Evolution, and Systematics
StatePublished - Dec 1 2009

All Science Journal Classification (ASJC) codes

  • Ecology, Evolution, Behavior and Systematics
  • Ecology


  • Global biogeochemistry
  • Nitrogen cycle
  • Nitrogen fixation
  • Nutrients
  • Phosphorus
  • Tropical forests


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