The role of ammonia volatilization in controlling the natural 15N abundance of a grazed grassland

Douglas Alan Frank, R. David Evans, Benjamin F. Tracy

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Abstract

Although the variation in natural 15N abundance in plants and soils is well characterized, mechanisms controlling N isotopic composition of organic matter are still poorly understood. The primary goal of this study was to examine the role of NH3 volatilization from ungulate urine patches in determining 15N abundance in grassland plants and soil in Yellowstone National Park. We additionally used isotopic measurements to explore the pathways that plants in urine patches take up N. Plant, soil, and volatilized NH3 §15N were measured on grassland plots for 10 days following the addition of simulated urine. Simulated urine increased 15N of roots and soil and reduced 15N of shoots. Soil enrichment was due to the volatilization of isotopically light NH 3. Acid-trapped NH3 §15N increased from -28‰ (day 1) to -0.3‰ (day 10), and was lighter than the original urea-N added (1.2‰). A mass balance analysis of urea-derived N assimilated by plants indicated that most of the N taken up by plants was in the form of ammonium through roots. However, isotope data also showed that shoots directly absorbed 15N - depleted NH3-N that was volatilized from simulated urine patches. These results indicate that NH 3 volatilization from urine patches enriches grassland soil with 15N and shoots are a sink for volatilized NH3, which likely leads to accelerated cycling of excreted N back to herbivores.

Original languageEnglish (US)
Pages (from-to)169-178
Number of pages10
JournalBiogeochemistry
Volume68
Issue number2
DOIs
StatePublished - Apr 2004

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Keywords

  • N
  • Ammonia
  • Grassland
  • Herbivory
  • Ungulate
  • Volatilization
  • Yellowstone National Park

ASJC Scopus subject areas

  • Earth and Planetary Sciences (miscellaneous)
  • Environmental Science(all)

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