Journal of Soils and Sediments

, Volume 18, Issue 4, pp 1303–1313 | Cite as

Selective effects of forest fires on the structural domains of soil humic acids as shown by dipolar dephasing 13C NMR and graphical-statistical analysis of pyrolysis compounds

  • Gonzalo Almendros
  • Pilar Tinoco
  • José-María De la Rosa
  • Heike Knicker
  • José-Antonio González-Pérez
  • Francisco J. González-Vila
Natural Organic Matter: Chemistry, Function and Fate in the Environment



Data management strategies of pyrolysis results and NMR acquisition modes were examined in humic acids (HAs) from control soils and fire-affected soils. The information supplied by dipolar dephasing (DD) 13C NMR spectroscopy and Curie-point pyrolysis were used to assess chemical structures hardly recognizable and measurable, or of unclear interpretation, when using 13C NMR under standard acquisition pulses (cross-polarization/magic angle spinning, CPMAS).

Materials and methods

The HAs were isolated from two forest soils under Pinus halepensis and Pinus sylvestris in control and burned sites affected by medium or severe-intensity wildfires. For NMR analyses, during DD acquisition conditions, a 180° 13C pulse was inserted to minimize phase shifts. Curie-Point pyrolysis was carried out at 510 °C for 5 s, and the pyrolysis fragments were analyzed by GC/MS. The total abundances of the major pyrolysis products were compared by an update of the classical Van Krevelen’s graphical-statistical approach, i.e., as surface density values in the space defined by the compound-specific H/C and O/C atomic ratios.

Results and discussion

The DD 13C NMR experiments displayed significant differences in the HA spectral profiles as regards to the standard CPMAS 13C NMR acquisition conditions, mainly in the chemical shift region of alkyl structures as well as for tannin- or carbohydrate-like O-alkyl structures. In fact, the comparison between DD and CPMAS solid-state NMR suggested shortening of alkyl chains and generation of carbohydrate-derived, unsaturated structures—viz. furans—which adds to the aromatic domain. Pyrolytic results showed fire-induced specific changes in HAs chemical structure and its molecular diversity. The changes were evident in the location and sizes of the different clusters of pyrolysis compounds defined by their atomic ratios.


The DD 13C NMR provided specific information on the fate of aliphatic structures and the origin of unsaturated HA structures, which could be helpful in differentiating “inherited” from “pyrogenic” aromatic structures. This is further confirmed by the analysis of the molecular assemblages of pyrolytic products, which showed accumulation of condensed polyaromatic domains in the HAs after the high-intensity fire, accompanied by a recalcitrant alkyl hydrocarbon domain. Medium-intensity fire led to aromaticity increase due to a selective accumulation of lignin-derived phenols concomitant to the depletion of aliphatic hydrocarbon constituents.


Curie-point pyrolysis Dipolar dephasing Forest fires damage levels Humic acid structural changes NMR 



The contributions by three anonymous reviewers and the financial support by the Spanish CICyT (grant CGL2013-43845-P) are gratefully acknowledged.

Supplementary material

11368_2016_1595_MOESM1_ESM.pdf (534 kb)
ESM 1 (PDF 533 kb)


  1. Alemany LB, Grant DM, Alger TD, Pugmire RJ (1983) Cross polarization and magic angle sample spinning NMR spectra of model organic compounds. 3. Effect of the 13C-1H dipolar interaction on cross polarization and carbon-proton dephasing. J Am Chem Soc 105:6697–6704Google Scholar
  2. Almendros G, González-Vila FJ (2012) Wildfires, soil carbon balance and resilient organic matter in Mediterranean ecosystems. A review. Spanish J Soil Sci 2:8–33Google Scholar
  3. Almendros G, Knicker H, González-Vila FJ (2003) Rearrangement of carbon and nitrogen forms in peat after progressive thermal oxidation as determined by solid-state 13C- and 15N spectroscopy. Org Geochem 34:1559–1568CrossRefGoogle Scholar
  4. Almendros G, González-Vila FJ, Martin F, Fründ R, Lüdemann H-D (1992) Solid state NMR studies of fire-induced changes in the structure of humic substances. Sci Total Environ 118:63–74CrossRefGoogle Scholar
  5. Conte P, Spaccini R, Piccolo A (2004) State of the art of CPMAS 13C-NMR spectroscopy applied to natural organic matter. Prog Nucl Mag Res Spectrosc 44:215–223CrossRefGoogle Scholar
  6. Czimczik C, Preston CM, Schmidt MWI, Werner RA, Schulze E-D (2002) Effects of charring on mass, organic carbon, and stable carbon isotope composition of wood. Org Geochem 33:1207–1223CrossRefGoogle Scholar
  7. DeBano LF (2000) The role of fire and soil heating on water repellency in wildland environments: a review. J Hydrol 231/232:195–206CrossRefGoogle Scholar
  8. Duchaufour P (1987) Manual de Edafología. Masson, Barcelona, p 224Google Scholar
  9. Fründ R, Lüdemann H-D (1989) The quantitative analysis of solution- and CPMAS-C-13 NMR spectra of humic material. Sci Total Environ 81/82:157–168CrossRefGoogle Scholar
  10. González-Pérez JA, Almendros G, De la Rosa JM, González-Vila FJ (2014) Appraisal of polycyclic aromatic hydrocarbons (PAHs) in environmental matrices by analytical pyrolysis (Py-GC/MS). J Anal Appl Pyrolysis 109:1–8CrossRefGoogle Scholar
  11. González-Pérez JA, González-Vila FJ, Almendros G, Knicker H (2004) The effect of fire on soil organic matter—a review. Environ Intern 30:855–870CrossRefGoogle Scholar
  12. Graber ER, Tagger S, Wallach R (2009) Role of divalent fatty acid salts in soil water repellency. Soil Sci Soc Amer J 73:541–549CrossRefGoogle Scholar
  13. Hatcher PG (1987) Chemical structural studies of natural lignin by dipolar dephasing solid-state 13C nuclear magnetic resonance. Org Geochem 11:31–39Google Scholar
  14. Hatcher PG, Schnitzer M, Vassallo AM, Wilson MA (1989) The chemical structure of highly aromatic humic acids in three volcanic ash soils as determined by dipolar dephasing NMR studies. Geochim Cosmochim Acta 53:125–130Google Scholar
  15. Hu WG, Mao JD, Xing BS, Schmidt-Rohr K (2000) Poly(methylene) crystallites in humic substances detected by nuclear magnetic resonance. Environ Sci Technol 34:530–534CrossRefGoogle Scholar
  16. Jiménez-Morillo NT, de la Rosa JM, Waggoner D, Almendros G, González-Vila FJ, González-Pérez JA (2016a) Fire effects in the molecular structure of organic matter in soil size fractions under Quercus suber cover. Catena 145:266–273CrossRefGoogle Scholar
  17. Jiménez-Morillo NT, González-Pérez JA, Jordán A, Zavala LM, de la Rosa JM, Jiménez-González M, González-Vila FJ (2016b) Organic matter fractions controlling soil water repellency in sandy soils from the Doñana national park (SW Spain). Land Degrad Develop 27:1413–1423Google Scholar
  18. Knicker H (2007) How does fire affect the nature and stability of soil organic nitrogen and carbon? A review. Biogeochemistry 85:91–118CrossRefGoogle Scholar
  19. Knicker H (2011) Solid state CPMAS 13C and 15N NMR spectroscopy in organic geochemistry and how spin dynamics can either aggravate or improve spectra interpretation. Org Geochem 42:867–890CrossRefGoogle Scholar
  20. Knicker H, González-Vila FJ, Polvillo O, González-Pérez JA, Almendros G (2005) Fire-induced transformation of C- and N-forms in different organic soil fractions from a dystric Cambisol under a Mediterranean pine forest (Pinus pinaster). Soil Biol Biochem 37:701–718CrossRefGoogle Scholar
  21. Kögel-Knabner I (1993) Biodegradation and humification processes in forest soils. In: Bollag JM, Stotzky G (eds) Soil biochemistry, vol 8. Dekker, New York, pp. 101–135Google Scholar
  22. Kramer RW, Kujawinski EB, Hatcher PG (2004) Identification of black carbon derived structures in a volcanic ash soil humic acid by Fourier transform ion cyclotron resonance mass spectrometry. Environ Sci Technol 38:3387–3395CrossRefGoogle Scholar
  23. Maciel GE, Haw JF, Smith DH, Gabrielsen BC, Hatfield GR (1985) Carbon-13 nuclear magnetic resonance of herbaceous plants and their components, using cross polarization and magic-angle spinning. J Agric Food Chem 33:185–191CrossRefGoogle Scholar
  24. Miralles I, Piedra-Buena A, Almendros G, González-Vila FJ, González-Pérez JA (2015) Pyrolytic appraisal of the lignin signature in soil humic acids: assessment of its usefulness as carbon sequestration marker. J Anal Appl Pyrolysis 113:107–115CrossRefGoogle Scholar
  25. Monnier G, Turc L, Jeanson-Luusinang C (1962) Une méthode de fractionnement densimétrique par centrifugation des matières organiques du sol. Ann Agron 13:55–63Google Scholar
  26. Preston CM (1996) Applications of NMR to soil organic matter analysis: history and prospects. Soil Sci 161:144–166CrossRefGoogle Scholar
  27. Saiz-Jiménez C, de Leeuw JW (1986a) Chemical characterization of soil organic matter fractions by analytical pyrolysis-gas chromatography-mass spectrometry. J Anal Appl Pyrolysis 9:99–119CrossRefGoogle Scholar
  28. Saiz-Jiménez C, de Leeuw JW (1986b) Lignin pyrolysis products: their structures and their significance as biomarkers. Org Geochem 10:869–876CrossRefGoogle Scholar
  29. Skjemstad JO, Clark P, Golchin A, Oades HM (1997) Characterization of soil organic matter by solid state 13C NMR spectroscopy. In: Cadisch G, Giller KE (eds) Driven by nature: plant litter quality and decomposition. CAB International, Wallingford, pp. 253–271Google Scholar
  30. Smernik RJ, Oades JM (2001) Solid-state 13C-NMR dipolar dephasing experiments for quantifying protonated and non-protonated carbon in soil organic matter and model system. Eur J Soil Sci 52:103–120CrossRefGoogle Scholar
  31. Stevenson FJ (1994) Humus chemistry. Genesis, composition, reactions. Wiley, New York, p. 512 ISBN: 978-0-471-59474-1Google Scholar
  32. Tinoco P, Almendros G, González-Vila FJ (2002) Impact of the vegetation on the lignin pyrolytic signature of soil humic acids from Mediterranean soils. J Anal Appl Pyrolysis 64:407–420CrossRefGoogle Scholar
  33. Van Krevelen DW (1950) Graphical-statistical method for the study of structure and reaction processes of coal. Fuel 29:269–284Google Scholar
  34. Walkley A, Black IA (1934) An examination of the Degtjareff method for determining soil organic matter, and a proposed modification of the chromic acid titration method. Soil Sci 37:29–38CrossRefGoogle Scholar
  35. Wilson MA (1987) NMR techniques and applications in geochemistry and soil chemistry. Pergamon, Oxford, p. 352 ISBN-13:978-0080348520Google Scholar
  36. Wilson MA, Hatcher PG (1988) Detection of tannins in modern and fossil barks and in plant residues by high-resolution solid-state 13C nuclear magnetic resonance. Org Geochem 12:539–546CrossRefGoogle Scholar
  37. WRB (2006) World Reference Base for soil resources 2006. World soil resources reports 103. FAO, RomeGoogle Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 2016

Authors and Affiliations

  • Gonzalo Almendros
    • 1
  • Pilar Tinoco
    • 2
  • José-María De la Rosa
    • 3
  • Heike Knicker
    • 3
  • José-Antonio González-Pérez
    • 3
  • Francisco J. González-Vila
    • 3
  1. 1.MNCN (CSIC)MadridSpain
  2. 2.University Alfonso X el SabioMadridSpain
  3. 3.Instituto de Recursos Naturales y Agrobiología de Sevilla (IRNAS-CSIC)SevilleSpain

Personalised recommendations