, Volume 138, Issue 1, pp 69–83 | Cite as

Amino acid δ15N indicates lack of N isotope fractionation during soil organic nitrogen decomposition

  • Michael PhilbenEmail author
  • Sharon A. Billings
  • Kate A. Edwards
  • Frances A. Podrebarac
  • Geert van Biesen
  • Susan E. Ziegler


The interpretation of natural abundance δ15N in soil profiles and across ecosystems is confounded by a lack of understanding of possible N isotope fractionation associated with soil organic nitrogen (SON) decomposition. We analyzed the δ15N of hydrolysable amino acids to test the extent of fractionation associated with the depolymerization of peptides to amino acids and the mineralization of amino acids to NH4+ (ammonification). Most amino acids are both synthesized and degraded by microbes, complicating interpretation of their δ15N. However, the “source” amino acids phenylalanine and hydroxyproline are degraded and recycled but not resynthesized. We therefore used their δ15N to isolate the effects of N isotope fractionation during SON depolymerization and ammonification. We used complementary field and laboratory approaches to evaluate the change in amino acid δ15N during decomposition. First, we measured amino acid δ15N changes with depth in the organic horizons of podzolic soils collected from the Newfoundland and Labrador Boreal Ecosystem Latitudinal Transect (NL-BELT), Canada. The δ15N of most amino acids increased with depth by 3–7‰, similar to the increase in bulk δ15N. However, the δ15N of the “source” amino acids did not change with depth, indicating lack of N isotope fractionation during their depolymerization and ammonification. Second, we assessed the change in amino acid δ15N following 400 days of laboratory incubation. This approach isolated the effect of decomposition on δ15N by eliminating plant N uptake and reducing leaching of N from the soil. Amino acid δ15N did not change during incubation despite extensive turnover of the amino acid pool, supporting our conclusion of a lack of N isotope fractionation during SON decomposition. Our results indicate the often-observed trend of increasing δ15N with soil depth likely results from the mycorrhizally-mediated transfer of 14N from depth to the surface and accumulation of 15N-enriched necromass of diverse soil microbes at depth, rather than as a direct result of SON decomposition.


Soil organic nitrogen Ammonification δ15Amino acid stable isotopes Nitrogen isotope fractionation 



We thank Jerome Laganière, Thalia Soucy-Giguere, and Julia Ferguson for assistance with soil collection, preparation, and incubations. We also thank Jamie Warren, Catie Young, Andrea Skinner, Darrell Harris, Rachelle Dove, Alison Pye, and Amanda Baker for field and laboratory assistance. Helpful comments from two anonymous reviewers improved the manuscript. This research was funded by the National Science and Engineering Councils of Canada Discovery Grants program and Strategic Project Grants program (#397494-10), Centre for Forest Science and Innovation of the Newfoundland and Labrador Agrifoods Agency, Canada Research Chairs Programme, and the Canadian Forest Service of Natural Resources Canada.


  1. Amundson R, Austin AT, Schuur EAG et al (2003) Global patterns of the isotopic composition of soil and plant nitrogen. Glob Biogeochem Cycles 17:31/1–31/10. CrossRefGoogle Scholar
  2. Bada JL, Schoeninger MJ, Schimmelmann A (1989) Isotopic fractionation during peptide bond hydrolysis. Geochim Cosmochim Acta 53:3337–3341. CrossRefGoogle Scholar
  3. Billings SA, Richter DD (2006) Changes in stable isotopic signatures of soil nitrogen and carbon during 40 years of forest development. Oecologia 148:325–333. CrossRefGoogle Scholar
  4. Boddey RM, Peoples MB, Palmer B, Dart PJ (2000) Use of the 15 N natural abundance technique to quantify biological nitrogen fixation by woody perennials. Nutr Cycl Agroecosyst 57:235–270. CrossRefGoogle Scholar
  5. Bol R, Ostle N, Chenu C et al (2004) Long term changes in the distribution and delta(15)N values of individual soil amino acids in the absence of plant and fertiliser inputs. Isot Environ Health Stud 40:243–256. CrossRefGoogle Scholar
  6. Brahney J, Ballantyne AP, Turner BL et al (2014) Separating the influences of diagenesis, productivity and anthropogenic nitrogen deposition on sedimentary δ15 N variations. Org Geochem 75:140–150. CrossRefGoogle Scholar
  7. Cheng S-L, Fang H-J, Yu G-R et al (2010) Foliar and soil 15 N natural abundances provide field evidence on nitrogen dynamics in temperate and boreal forest ecosystems. Plant Soil 337:285–297. CrossRefGoogle Scholar
  8. Chikaraishi Y, Kashiyama Y, Ogawa NO et al (2007) Metabolic control of nitrogen isotope composition of amino acids in macroalgae and gastropods: implications for aquatic food web studies. Mar Ecol Prog Ser 342:85–90. CrossRefGoogle Scholar
  9. Chikaraishi Y, Ogawa NO, Kashiyama Y et al (2009) Determination of aquatic food-web structure based on compound-specific nitrogen isotopic composition of amino acids. Limnol Oceanogr Methods 7:740–750. CrossRefGoogle Scholar
  10. Corr LT, Berstan R, Evershed RP (2007) Optimisation of derivatisation procedures for the determination of δ13C values of amino acids by gas chromatography/combustion/isotope ratio mass spectrometry. Rapid Commun Mass Spectrom 21:3759–3771. CrossRefGoogle Scholar
  11. Craine J, Craine JM, Elmore AJ et al (2009) Global patterns of foliar nitrogen isotopes and their relationships. New Phytol 183:980–992. CrossRefGoogle Scholar
  12. Craine JM, Elmore AJ, Wang L et al (2015) Convergence of soil nitrogen isotopes across global climate gradients. Sci Rep 5:8280. CrossRefGoogle Scholar
  13. Dijkstra P, Ishizu A, Doucett R et al (2006) 13C and 15 N natural abundance of the soil microbial biomass. Soil Biol Biochem 38:3257–3266. CrossRefGoogle Scholar
  14. Emmerton KS, Callaghan TV, Jones HE et al (2001) Assimilation and isotopic fractionation of nitrogen by mycorrhizal fungi. New Phytol 151:503–511. CrossRefGoogle Scholar
  15. Evans RD (2001) Physiological mechanisms influencing plant nitrogen isotope composition. Trends Plant Sci 6(3):121–126. CrossRefGoogle Scholar
  16. Fogel ML, Tuross N (1999) Transformation of plant biochemicals to geological macromolecules during early diagenesis. Oecologia 120:336–346. CrossRefGoogle Scholar
  17. Garten CT (1993) Variation in foliar 15 N abundance and the availability of soil nitrogen on walker branch watershed. Ecology 74:2098–2113. CrossRefGoogle Scholar
  18. Handley LL, Raven JA (1992) The use of natural abundance of nitrogen isotopes in plant physiology and ecology. Plant, Cell Environ 15:965–985. CrossRefGoogle Scholar
  19. He X, Xu M, Qiu GY, Zhou J (2009) N stable isotope to quantify nitrogen transfer between mycorrhizal plants. J Plant Ecol 2:107–118. CrossRefGoogle Scholar
  20. Hill PW, Farrar J, Roberts P et al (2011) Vascular plant success in a warming Antarctic may be due to efficient nitrogen acquisition. Nat Clim Change 1:50–53. CrossRefGoogle Scholar
  21. Hobbie E, Högberg P (2012) Nitrogen isotopes link mycorrhizal plants to nitrogen dynamics (supporting info). New Phytol 196:367–382CrossRefGoogle Scholar
  22. Hobbie EA, Ouimette AP (2009) Controls of nitrogen isotope patterns in soil profiles. Biogeochemistry 95:355–371. CrossRefGoogle Scholar
  23. Hogberg P (1997) Tansley review no. 95. 15 N natural abundance in soil-plant systems. New Phytol 137:179–203. CrossRefGoogle Scholar
  24. Holtgrieve GW, Schindler DE, Hobbs WO et al. (2011) A coherent signature of anthropogenic nitrogen deposition to remote watersheds of the Northern Hemisphere. Science 334:1545–1548CrossRefGoogle Scholar
  25. Houlton BZ, Bai E (2009) Imprint of denitrifying bacteria on the global terrestrial biosphere. Proc Natl Acad Sci USA 106:21713–21716. CrossRefGoogle Scholar
  26. Houlton BZ, Sigman DM, Hedin LO (2006) Isotopic evidence for large gaseous nitrogen losses from tropical rainforests. Proc Natl Acad Sci 103:8745–8750. CrossRefGoogle Scholar
  27. Junium CK, Arthur MA, Freeman KH (2015) Compound-specific δ15 N and chlorin preservation in surface sediments of the Peru Margin with implications for ancient bulk δ15 N records. Geochim Cosmochim Acta 160:306–318. CrossRefGoogle Scholar
  28. Kielland K, McFarland J, Olson K (2006) Amino acid uptake in deciduous and coniferous taiga ecosystems. Plant Soil 288:297–307. CrossRefGoogle Scholar
  29. Kohl L, Philben M, Edwards KA et al (2017) The origin of soil organic matter controls its composition and bioreactivity across a mesic boreal forest latitudinal gradient. Glob Change Biol. Google Scholar
  30. Kolb KJ, Evans RD (2003) Influence of nitrogen source and concentration on nitrogen isotopic discrimination in two barley genotypes (Hordeum vulgare L.). Plant, Cell Environ 26:1431–1440. CrossRefGoogle Scholar
  31. Laganière J, Podrebarac F, Billings SA et al (2015) A warmer climate reduces the bioreactivity of isolated boreal forest soil horizons without increasing the temperature sensitivity of respiratory CO2 loss. Soil Biol Biochem 84:177–188. CrossRefGoogle Scholar
  32. Macko SA, Estep ML (1984) Microbial alteration of stable nitrogen and carbon isotopic compositions of organic matter. Org Geochem 6:787–790. CrossRefGoogle Scholar
  33. Macko SA, Fogel ML, Hare PE, Hoering TC (1987) Isotopic fractionation of nitrogen and carbon in the synthesis of amino acids by microorganisms. Chem Geol Isot Geosci Sect 65:79–92. CrossRefGoogle Scholar
  34. McCarthy MD, Benner R, Lee C, Fogel ML (2007) Amino acid nitrogen isotopic fractionation patterns as indicators of heterotrophy in plankton, particulate, and dissolved organic matter. Geochim Cosmochim Acta 71:4727–4744. CrossRefGoogle Scholar
  35. McClelland JW, Montoya JP (2002) Trophic relationships and the nitrogen isotopic composition of amino acids in plankton. Ecology 83:2173–2180.[2173:TRATNI]2.0.CO;2 CrossRefGoogle Scholar
  36. Melillo JM, Aber JD, Linkins AE et al (1989) Carbon and nitrogen dynamics along the decay continuum: plant litter to soil organic matter. Plant Soil 115:189–198. CrossRefGoogle Scholar
  37. Merritt DA, Hayes JM (1994) Nitrogen isotopic analyses by isotope-ratio-monitoring gas chromatography/mass spectrometry. J Am Soc Mass Spectrom 5:387–397. CrossRefGoogle Scholar
  38. Möbius J (2013) Isotope fractionation during nitrogen remineralization (ammonification): implications for nitrogen isotope biogeochemistry. Geochim Cosmochim Acta 105:422–432. CrossRefGoogle Scholar
  39. Natelhoffer KJ, Fry B (1988) Controls on natural nitrogen-15 and carbon-13 abundances in forest soil organic matter. Soil Sci Soc Am J 52:1633. CrossRefGoogle Scholar
  40. O’Connell TC (2017) 'Trophic' and 'source' amino acids in trophic estimation: a likely metabolic explanation. Oecologia 184:317–326CrossRefGoogle Scholar
  41. Philben M, Benner R (2013) Reactivity of hydroxyproline-rich glycoproteins and their potential as biochemical tracers of plant-derived nitrogen. Org Geochem 57:11–22. CrossRefGoogle Scholar
  42. Philben M, Ziegler SE, Edwards KA et al (2016) Soil organic nitrogen cycling increases with temperature and precipitation along a boreal forest latitudinal transect. Biogeochemistry 127:397–410. CrossRefGoogle Scholar
  43. Podrebarac FA, Laganière J, Billings SA et al (2016) Soils isolated during incubation underestimate temperature sensitivity of respiration and its response to climate history. Soil Biol Biochem 93:60–68. CrossRefGoogle Scholar
  44. Robinson D (2001) δ15 N as an integrator of the nitrogen cycle. Trends Ecol Evol 16:153–162. CrossRefGoogle Scholar
  45. Schimel JP, Bennett J (2004) Nitrogen mineralization: challenges of a changing paradigm. Ecology 85:591–602. CrossRefGoogle Scholar
  46. Silfer JA, Engel MH, Macko SA (1992) Kinetic fractionation of stable carbon and nitrogen isotopes during peptide bond hydrolysis: experimental evidence and geochemical implications. Chem Geol Isot Geosci Sect 101:211–221. CrossRefGoogle Scholar
  47. Snider DM, Venkiteswaran JJ, Schiff SL, Spoelstra J (2015) From the ground up: global nitrous oxide sources are constrained by stable isotope values. PLoS ONE 10:e0118954. CrossRefGoogle Scholar
  48. Steffan SA, Chikaraishi Y, Horton DR et al (2013) Trophic hierarchies illuminated via amino acid isotopic analysis. PLoS ONE 8:e76152. CrossRefGoogle Scholar
  49. Steffan SA, Chikaraishi Y, Currie CR et al (2015) Microbes are trophic analogs of animals. Proc Natl Acad Sci 112:15119–15124. CrossRefGoogle Scholar
  50. Trappe JM (1962) Fungus associates of ectotrophic mycorrhizae. Bot Rev 28:538–606. CrossRefGoogle Scholar
  51. Tremblay L, Benner R (2006) Microbial contributions to N-immobilization and organic matter preservation in decaying plant detritus. Geochim Cosmochim Acta 70:133–146. CrossRefGoogle Scholar
  52. Vitousek PM, Menge DNL, Reed SC, Cleveland CC (2013) Biological nitrogen fixation: rates, patterns and ecological controls in terrestrial ecosystems. Philos Trans R Soc B Biol Sci 368:20130119. CrossRefGoogle Scholar
  53. Ziegler SE, Benner R, Billings SA et al (2017) Climate warming can accelerate carbon fluxes without changing soil carbon stocks. Front Earth Sci. Google Scholar

Copyright information

© Springer International Publishing AG, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Department of Earth SciencesMemorial UniversitySt. John’sCanada
  2. 2.Department of Ecology and Evolutionary Biology, Kansas Biological SurveyUniversity of KansasLawrenceUSA
  3. 3.Natural Resources Canada, Canadian Forest ServiceAtlantic Forestry CentreCorner BrookCanada
  4. 4.CREAIT - Stable Isotope LaboratoryMemorial UniversitySt. John’sCanada
  5. 5.Environmental Sciences DivisionOak Ridge National LaboratoryOak RidgeUSA
  6. 6.United State Department of AgricultureNatural Resources Conservation ServiceColumbusUSA

Personalised recommendations