Pyrolysis-gas chromatography, mass spectrometry characterization of humic acids in coastal spodosols from Southeastern Brazil

Abstract

This study on humic acids (HAs) of podzol horizons from the southeastern region of Brazil investigated the accumulation and degradation of soil organic matter (SOM) in warm-climate podzols. Humic acids from sandy coastal Spodosols (Histic Alaquod and Arenic Alorthod) from Cardoso Island in Sao Paulo State were characterized by pyrolysis in combination with gas chromatography and mass spectrometry (Py-GC/MS). The soils developed on quartziticsandynutrient-poor parent materials under restinga forest in a coastal area. The Py-GC/MS results show that the chemical composition of HAs in B horizons in one out of three profiles was influenced by both dissolved organic C (DOC) and C from in situ decaying roots. Carbon derived from DOC dominated in the deepest part of the B horizons. In the Arenic Alorthod (H9) profileSOM from the B horizon seemed to be largely derived from roots. The DOC-derived SOM was characterized by large contributions of phenolmethylphenolsand degraded polysaccharide productswhile root contributions were mainly characterized by lignin products. Aliphatics were most abundant in A horizons (E and EB horizons were not analyzed). Both DOC-derived and lignin-derived SOM showed distinct degradation patterns. The Py-GC/MS results corroborate those obtained by 13C variable amplitude cross polarization magic angle spinning nuclear magnetic resonance spectroscopy and Fourier-transform infrared spectroscopy. Molecular chemistry showed that podzol B horizons are variable in compositionand local influences such as drainage and vertical or lateral water transportand SOM decomposition play an important role in podzolization processes in warm climates.


Reference:
GONZALEZ-PEREZ, Martha; BUURMAN, P.; VIDAL-TORRADO, P.; MARTIN NETO, L. Pyrolysis-gas chromatography, mass spectrometry characterization of humic acids in coastal spodosols from Southeastern Brazil. Soil Science Society of America Journal, v. 76, n. 3, p. 961-971, may-jun., 2012.

Access to the website of the Journal Article:

https://www.soils.org/publications/sssaj/pdfs/76/3/961

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