BUURMAN, P.

GONZÁLEZ-PÉREZ, M.

MARTIN NETO, L.

VIDAL-TORRADO, P.

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15th 1HSS Meeting- VaI. 2Pyrolysis-Gas Chromatography/Mass Spectrometry Characterization ofHumic Acids in Spodosols Under Tropical Rain Forest in SoutheasternBrazilMartha Gonzalez-Pérez':", Peter Buurman", Pablo Vidal- Torrado", Ladislau Martin-NetobaEscola Superior de Agricultura "Luiz de Queiroz" (ESALQ-USP). Departamento de Ciênciado Solo. C.P. 09, CEP 13418-900 Piracicaba-SP, Brazil. 'Embrapa InstrumentaçãoAgropecuária, C.P.741, CEP: 13560-970, São Carlos, SP, Brazil. CEarth System Sciences andClimate Change Group. Department ofEnvironmental Sciences. Wageningen University.P.O. Box 47.6700 AA. Wageningen. The Netherlands.E-mail: marta@cnpdia.embrapa.br1. IntroductionThe present study aims to contribute to a better understanding of the podzolization processesin intrazonal tropical podzols, specifically in the Restinga forest of São Paulo state.Podzolization is the main pedogenic process in Restinga and the most common soils areSpodosols (podzols) and Quartzipsamments (Arenosols) with incipient podzolization. Thisstudy addresses the same samples that were earlier studied by González-Pérez et a\. [1] by I3CNuclear Magnetic Resonance Spectroscopy using Variable Amplitude Cross Polarization andMagic Angle Spinning Technique (l3C VACP/MAS NMR) and by Fourier TransformInfrared Spectroscopy (FTIR). Pyrolysis in combination with gas chromatography and massspectrometry (Py-GCIMS) adds to previous results information about molecular fragments,individual structures such as polysaccharides, lignin moieties, and fatty acids. This latterinformation can be used to reconstruct the origin (microbial, plant-derived, specific species),degradation mode, degradation state of the SOM and also their role in podzolization process[2, 3]. Although HAs constitute only part of the SOM in podzols, it is expected thatconclusions based on this fraction can be extrapolated to the total SOM.2. Materiais and MethodsGeneral comments on soils and previous analysisThree of the sandy spodosols of Cardoso Island (a Natural Park in the State of São Paulo,Southeast - Brazil) under Restinga forest, were selected for this study. Profile H 13 is a HisticAlaquod, profile C 14 is a Typic Alorthod, and profile H9 is an Arenic Alorthod [4]. Thehorizon sequences are given in Table 1. Ali profiles are hydromorphic and virtually irondepleted.VaI. 2 Page - 329-15th 1HSS Meeting- VaI. 2Table I: Particle size fractions and some chemical properties ofthe three profilesSoil/ Depth Sand Silt Clay pH C/Me C N C/NHorizon k -I H20 k -Iem -------------g g ---------- ------g g ------Profile H13 - Histic AlaquodHo 0-10 n. d. n. d. n. d. 3.8 14.9 319.0 15.3 20.9Hd 10-20 n. d. n. d. n. d. 4.0 40.5 241.0 5.4 44.6AI 20-30 n. d. n. d. n. d. 4.2 40.5 68.9 1.0 68.9E 30-38 970 O 30 4.3 0.0 4.7 0.5 9.4Bhsl 38-55 970 O 30 3.3 13.5 30.3 0.9 33.7Bhs2 55-75 960 O 40 3.2 11.1 15.5 0.4 38.8Bhs3 75-130 950 10 40 3.3 6.1 8.8 0.5 17.6Profile C14 - Typic AlorthodA 0-15 960 O 40 4.3 12.4 35.8 1.9 18.8AE 15-20 980 O 20 4.3 16.0 2.2 0.3 7.3E 20-50 980 10 10 5.0 0.0 0.3 0.3 1.0Bhsl 50-58 920 O 80 4.0 14.8 37.4 1.4 26.7Bhs2 58-75 900 O 100 4.0 10.4 64.2 1.9 33.8Bhs3 75-100 920 10 70 4.8 2.5 17.5 0.8 21.9BsI 100-120 910 30 60 4.8 1.4 9.8 0.8 12.3Profile H9 - Arenic AlorthodA 0-20 970 O 30 4.7 28.8 16.4 1.0 16.4AE 20-28 980 O 20 4.6 75.0 2.9 0.7 4.1EI 28-41 980 O 20 4.8 80.0 0.8 0.2 4.0E2 41-95 980 O 20 5.0 80.0 0.3 0.2 1.5Bhsl 95-103 940 10 50 4.2 9.9 28.6 1.1 26.0Bhs2 103-130'140 950 10 40 3.4 9.1 17.1 0.8 21.4Bhs3 130'140-180+-960 10 30 3.4 5.4 9.0 0.5 18.0lelMe = carbon/metalratio;Me=Als+Fe,Description ofthe area, morphology of profiles and chemical and mineralogical data are givenby Gomes et aI. [5]. Micromorphological characteristics, the procedure used for extractionand purification of humic acids, and the results of I3C VACPIMAS NMR and FTIRspectroscopy are described in a previous paper [1].Pyrolysis- Gas Chromatography/mass-spectrometry (Py-GC/MS)Humic acids were pyrolyzed using a Horizon Instruments Curie-Point pyrolyzer (Curietemperature of 600°C) connected to a Carlo Erba gas chromatograph. The pyrolysis productswere separated on a fused silica co\umn (Chrompack 25 m, 0.25 mm i.d.) coated with CP-Sil51b (film thickness 0.40 um), Helium was used as carrier gas. The initial oven temperaturewas 40°C with a heating rate of 7 °C min'. The final temperature of 320°C was maintainedfor 20 min. The GC co\umn was connected to a Fisons MD800 mass spectrometer (massVaI. 2 Page - 330-15th lHSS Meeting- VaI. 2range m/z 45-650, cycle time 1s). Products were identified using the internal NIST library andpublished sources [6, 7].Statistical analysisFactor analysis was carried out using Statistica Version 6 (StatSoft, Tulsa, UK). Factoranalysis allows the recognition of correlations between variables and the detection ofstructures in the data set. It is a prime method to reduce the number of variables and toc1assify variables.3. Results and DiscussionThe 136 different pyrolysis products were identified in ali samples and quantified using thetwo main fragment ions of each compound. Pyrolytic compounds were grouped according toprobable origin and chemical similarity. The dominant groups in ali horizons are aromatics,lignins and phenols, but there is significant variation within and between profiles. There donot appear to be consistent depth trends for any ofthe chemical groups.Factor analysis was carried out using ali 136 quantified pyrolysis products for the 15 samples.Two factors explained 53.2% of ali variation, while four factors explained 72.9%.Micromorphology indicates that horizons Bhs3 and Bsl ofprofile C14 are fully dominated bymonomorphic (DOC-derived) organic matter. The Bhs2 and Bhs3 horizons of profile 9 have alarge amount of roots in various stages of decomposition. The other B-horizons have varyingamounts of-Iargely decomposed-roots. These observations are in agreement with the plotof samples in the Factor score Diagram.The Py-GC/MS results corroborate those obtained by 13C VACPIMAS NMR and FTIR[1].This is especially true for the following features:• The highly aliphatic character in the topsoil of profile H13.• The high aromatic (Iignin) content in the lower horizons ofprofile H9.• Similarities among chemical composition ofB horizons ofprofiles H13 and C14 andtheir differences with profile H9.In addition, the pyrolysis data give reliable information conceming the relative amounts ofDOC- and root-derived SOM. There appear to be degradation paths for alkanes and alkenes(shorter chain lengths), lignins (Ioss of methoxyls and OH-groups) and phenols (loss of OHgroups). Aerobic decay in topsoils appears to lead to a relative accumulation of aliphatics.Vai. 2 Page - 331 -15th 1HSS Meeting- VaI. 2This is not clearly illustrated by the present samples because E-horizons and EB horizonshave not been sampled. Anaerobic decay in subsoils, on the other hand, appears to lead to arelative accumulation of methylbenzenes and degraded polysaccharides at the expense oflignin and phenols.4. ConclusionsAlthough morphological description of the three profiles did not indicate major differences,the chemical composition of the HAs obtained from pyrolysis data in the B horizons ofprofiles HI3 and C14 ofthe three profiles was dominated by dissolved organic carbon, whilethe profile H9 was dominated by root-derived material. A dominance of DOC is witnessedespecially by high abundances of phenol, methylphenols, and acetic acid. Some B horizonsshow a very strong degradation ofthe accumulated DOC. The cause ofthis degradation is stillunclear. In hydromorphic podzols such as the ones studied here, both vertical and lateral DOCtransport play a role in SOM accumulation in the B horizon. The morphology of profiles H13and C 14 suggests a major influence of lateral transporto Except for the two deepest horizonsof profile C14, ali horizons show chemical (and micromorphological) evidence of root-derived OM. Therefore, also in these tropical and largely badly drained podzols, both SOMilluviation and decay ofroots play a large role in the accumulation ofB-horizon OM.AcknowledgementsThe study was financed by The State of São Paulo Research Foundation, FAPESP, Brazil,Grant # 06/52408-0 and project # 04/03477-3. We thank Mr. EJ. Velthorst, BSc ofWageningen University, for preparing the pyrograms.References1. González Pérez, M., Vidal-Torrado, P., Colnago, L.A., Martin-Neto, L., Otero, X.L.,Milori, D.M.B.P., Gomes, F.H. Geoderma, 146,425-433,2008.2. Buurman, P., Petersen, F., Almendros, G. Eur. J. Soil Sei., 58, 1330-1347,2007.3. Schellekens, J., Buurman, P., Pontevedra-Pornbal, X. Org. Geochem., 40, 678-691,2009.4. Soil Survey Staff. 1999. Soi! Taxonomy: A Basic System ofSoil ClassificationforMaking and Interpreting Soil Surveys. USDA, Agricultural Handbook,N.436.Washington, DC (USA). 2nd edition. 869p.5. Gomes, F.H., Vidal-Torrado, P., Macías, F., Gherardi, B., Otero, X. L. R. Bras. ct. Solo,31(6),1563-1580,2007.6. Ralph, J., Hatfield, R.D. J. Agric. Food Chem., 39, 1426-1437, 1991.7. Nierop, K.GJ., van Lagen, B., Buurman, P. Geoderma, 100, 1-24,2001.VaI. 2 Page - 332 -

Pyrolysis-gas chromatography/mass spectrometry characterization of humic acids in spodosols under tropical rain forest in southeastern Brazil.

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