Oecologia

, Volume 163, Issue 4, pp 1069–1078 | Cite as

Amino acid abundance and proteolytic potential in North American soils

  • Kirsten S. Hofmockel
  • Noah Fierer
  • Benjamin P. Colman
  • Robert B. Jackson
Ecosystem ecology - Original Paper

Abstract

Studies of nitrogen (N) cycling have traditionally focused on N mineralization as the primary process limiting plant assimilation of N. Recent evidence has shown that plants may assimilate amino acids (AAs) directly, circumventing the mineralization pathway. However, the general abundance of soil AAs and their relative importance in plant N uptake remains unclear in most ecosystems. We compared the concentrations and potential production rates of AAs and NH4+, as well as the edaphic factors that influence AA dynamics, in 84 soils across the United States. Across all sites, NH4+ and AA-N comprised similar proportions of the total bioavailable N pool (~20%), with NO3 being the dominant form of extractable N everywhere but in tundra and boreal forest soils. Potential rates of AA production were at least comparable to those of NH4+ production in all ecosystems, particularly in semi-arid grasslands, where AA production rates were six times greater than for NH4+ (P < 0.01). Potential rates of proteolytic enzyme activity were greatest in bacteria-dominated soils with low NH4+ concentrations, including many grassland soils. Based on research performed under standardized laboratory conditions, our continental-scale analyses suggest that soil AA and NH4+ concentrations are similar in most soils and that AAs may contribute to plant and microbial N demand in most ecosystems, particularly in ecosystems with N-poor soils.

Keywords

Soil N cycle Proteolysis Ammonium Amino acid Organic N Nitrification Nitrogen mineralization Protein mineralization 

Supplementary material

442_2010_1601_MOESM1_ESM.doc (209 kb)
Supplementary material 1 (DOC 209 kb)

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Copyright information

© Springer-Verlag 2010

Authors and Affiliations

  • Kirsten S. Hofmockel
    • 1
    • 2
  • Noah Fierer
    • 3
    • 4
  • Benjamin P. Colman
    • 5
    • 6
  • Robert B. Jackson
    • 1
    • 6
  1. 1.Nicholas School of the Environment and Earth SciencesDuke UniversityDurhamUSA
  2. 2.Department of Ecology, Evolution and Organismal BiologyIowa State UniversityAmesUSA
  3. 3.Cooperative Institute for Research in Environmental SciencesUniversity of Colorado at BoulderBoulderUSA
  4. 4.Department of Ecology and Evolutionary BiologyUniversity of Colorado at BoulderBoulderUSA
  5. 5.Department of Ecology, Evolution, and Marine BiologyUniversity of CaliforniaSanta BarbaraUSA
  6. 6.Department of BiologyDuke UniversityDurhamUSA

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