Elevated CO2 and nutrient addition alter soil N cycling and N trace gas fluxes with early season wet-up in a California annual grassland

Bruce A. Hungate, Christopher P. Lund, Holly L. Pearson, F. Stuart Chapin

Research output: Contribution to journalArticlepeer-review

115 Scopus citations


We examined the effects of growth carbon dioxide (CO2) concentration and soil nutrient availability on nitrogen (N) transformations and N trace gas fluxes in California grassland microcosms during early-season wet-up, a time when rates of N transformation and N trace gas flux are high. After plant senescence and summer drought, we simulated the first fall rains and examined N cycling. Growth at elevated CO2 increased root production and root carbon:nitrogen ratio. Under nutrient enrichment, elevated CO2 increased microbial N immobilization during wet-up, leading to a 43% reduction in gross nitrification and a 55% reduction in NO emission from soil. Elevated CO2 increased microbial N immobilization at ambient nutrients, but did not alter nitrification or NO emission. Elevated CO2 did not alter soil emission of N2O at either nutrient level. Addition of NPK fertilizer (1:1:1) stimulated N mineralization and nitrification, leading to increased N2O and NO emission from soil. The results of our study support a mechanistic model in which elevated CO2 alters soil N cycling and NO emission: increased root production and increased C:N ratio in elevated CO2 stimulate N immobilization, thereby decreasing nitrification and associated NO emission when nutrients are abundant. This model is consistent with our basic understanding of how C availability influences soil N cycling and thus may apply to many terrestrial ecosystems.

Original languageEnglish (US)
Pages (from-to)89-109
Number of pages21
Issue number2
StatePublished - 1997


  • N
  • N pool dilution
  • NO
  • NO
  • NPK fertilizer
  • annual grassland
  • elevated CO
  • first autumn rains
  • gross mineralization
  • gross nitrification
  • trace gases

ASJC Scopus subject areas

  • Environmental Chemistry
  • Water Science and Technology
  • Earth-Surface Processes


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