Soil Organic Matter Molecular Composition Shifts Driven by Forest Regrowth or Pasture after Slash-and-Burn of Amazon Forest

Otávio dos Anjos Leal (), Nicasio T. Jiménez-Morillo, José A. González-Pérez, Heike Knicker, Falberni de Souza Costa, Pedro N. Jiménez-Morillo, João Andrade de Carvalho Júnior, José Carlos dos Santos and Deborah Pinheiro Dick
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Otávio dos Anjos Leal: Institute of Bio- and Geosciences—Agrosphere (IBG-3), Forschungszentrum Jülich GmbH, Wilhelm-Johnen-Straße, 52428 Jülich, Germany
Nicasio T. Jiménez-Morillo: Mediterranean Institute for Agriculture, Environment and Development-MED, Universidade de Évora, Ap 94, 7002-554 Évora, Portugal
José A. González-Pérez: Instituto de Recursos Naturales y Agrobiología de Sevilla (IRNAS-CSIC), Av. Reina Mercedes 10, 41012 Seville, Spain
Heike Knicker: Instituto de Recursos Naturales y Agrobiología de Sevilla (IRNAS-CSIC), Av. Reina Mercedes 10, 41012 Seville, Spain
Falberni de Souza Costa: Embrapa Acre, Rodovia BR-364, Km 14, Rio Branco 69900-970, Brazil
Pedro N. Jiménez-Morillo: Departamento de Sistemas Físicos, Químicos y Biológicos, Universidad Pablo de Olavide, Ctra. Utrera, 1, 41013 Seville, Spain
João Andrade de Carvalho Júnior: Departamento de Energia, Universidade Estadual Paulista, Av. Ariberto Pereira da Cunha, 333, Portal das Colinas, Guaratinguetá 12516-410, Brazil
José Carlos dos Santos: Laboratório Associado de Combustão e Propulsão, Instituto Nacional de Pesquisas Espaciais (INPE), Rodovia Presidente Dutra, km 40, Cachoeira Paulista 12630-00, Brazil
Deborah Pinheiro Dick: Departamento de Química, Universidade Federal do Rio Grande do Sul, Av. Bento Gonçalves, 9500, Porto Alegre 91501-970, Brazil

IJERPH, 2023, vol. 20, issue 4, 1-16

Abstract: Slash-and-burn of Amazon Forest (AF) for pasture establishment has increased the occurrence of AF wildfires. Recent studies emphasize soil organic matter (SOM) molecular composition as a principal driver of post-fire forest regrowth and restoration of AF anti-wildfire ambience. Nevertheless, SOM chemical shifts caused by AF fires and post-fire vegetation are rarely investigated at a molecular level. We employed pyrolysis–gas chromatography–mass spectrometry to reveal molecular changes in SOM (0–10, 40–50 cm depth) of a slash-burn-and-20-month-regrowth AF (BAF) and a 23-year Brachiaria pasture post-AF fire (BRA) site compared to native AF (NAF). In BAF (0–10 cm), increased abundance of unspecific aromatic compounds (UACs), polycyclic aromatic hydrocarbons (PAHs) and lipids (Lip) coupled with a depletion of polysaccharides (Pol) revealed strong lingering effects of fire on SOM. This occurs despite fresh litter deposition on soil, suggesting SOM minimal recovery and toxicity to microorganisms. Accumulation of recalcitrant compounds and slow decomposition of fresh forest material may explain the higher carbon content in BAF (0–5 cm). In BRA, SOM was dominated by Brachiaria contributions. At 40–50 cm, alkyl and hydroaromatic compounds accumulated in BRA, whereas UACs accumulated in BAF. UACs and PAH compounds were abundant in NAF, possibly air-transported from BAF.

Keywords: experimental burning; Brazilian Amazon; Brachiaria; n-alkanes; analytical pyrolysis; van Krevelen 3D diagrams; Acrisol (search for similar items in EconPapers)
JEL-codes: I I1 I3 Q Q5 (search for similar items in EconPapers)
Date: 2023
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