Molecular chemistry in humic Ferralsols from Brazilian Cerrado and forest biomes indicates a major contribution from black carbon in the subsoil

Autor(es)

Marques, Flavio Adriano ^[1] ; Buurman, Peter ^[2] ; Schellekens, Judith ^[3] ; Vidal-Torrado, Pablo ^[3]

Afiliação do(s) autor(es)

^[1] Embrapa Solos UEP Recife, BR-51020240 Recife, PE - Brazil

^[2] Wageningen Univ, Dept Environm Sci, Earth Syst Sci Grp, NL-6700 AA Wageningen - Netherlands

^[3] Escola Super Agr Luiz de Queiroz ESALQ USP, Dept Ciencia Solo, Sao Paulo - Brazil

• Tipo de documento: Artigo Científico
• Fonte: JOURNAL OF ANALYTICAL AND APPLIED PYROLYSIS; v. 113, p. 518-528, MAY 2015.
• Citações Web of Science: 10

Resumo

Soil organic matter (OM) stability plays an important role in the global carbon cycle. The molecular characterisation of soil OM may contribute to an understanding of the feedback mechanisms between soil OM and climate. Umbric Ferralsols with humic properties (humic Ferralsols) are characterised by a thick dark carbon-rich A horizon, and co-occur next to Umbric Ferralsols without humic characteristics. They are concentrated in south-eastern Brazil which suggests an environmental control. In order to understand OM stability in these soils, humic Ferralsols from three Brazilian biomes were studied, including Cerrado (savanna), subtropical forest and tropical forest. The studied soils were developed on several geological substrates, including basalt, gneiss, chamokites, phyllite and tertiary sediments. The molecular composition of the free light fraction (FLF), occluded light fraction (OLF) and 0.1 M NaOH extractable OM of samples from topsoil and subsoil from eight profiles was examined using analytical pyrolysis (pyrolysis-GC/MS). The light fraction reflects litter and charcoal, obtained by density fractionation before (FLF) and after (OLF) ultrasonic disruption; the NaOH extractable fraction (humic acid + fulvic acid) reflects more decomposed material. The chemical differences among soils from different Brazilian biomes were much smaller than the vertical gradient within each profile. The results showed that, within the light fractions, the content of which varied between 2% and 22% of the total carbon content (C-t), black carbon (BC) derived pyrolysis products showed a higher abundance in the topsoil. In the extractable OM, which varied between 46% and 88% of C-t, BC derived pyrolysis products showed a higher abundance in the subsoil. This suggests a continuous input of BC and an increase in the degree of decomposition with depth. Pyrolysis products associated with BC contributed up to 10% to the extractable pyrolysable fraction in the subsoil. The results suggest that degradation of charcoal, which is translocated to the subsoil by macroscopic soil organisms, results in a relative high contribution from naphthalene, 2-ethenylnaphthalene, phenanthrene, benzene, dibenzofuran and benzonitrile (subsoil) compared to (other) polyaromatic hydrocarbons (PAHs; C-1-, C-2- and C-3-naphthalenes and fluorene) in relatively fresh charcoal (topsoil). The results highlight the importance of the subsoil in studies of the long term effects of fire on soil OM and suggest that BC is an important factor that underlies carbon stability in humic Ferralsols. (C) 2015 Elsevier B.V. All rights reserved. (AU)

• Processo FAPESP: 13/03953-9 - Dinâmica da matéria orgânica em organossolos de turfeiras tropicais (Diamantina-MG, Brasil) - desenvolvimento de proxies moleculares para a reconstrução de mudanças paleoambientais
• Beneficiário: Judith Schellekens
• Modalidade de apoio: Bolsas no Brasil - Pós-Doutorado
• Processo FAPESP: 06/58068-6 - Latossolos com horizonte a humico: caracterizacao, distribuicao, genese e significado paleoambiental no territorio brasileiro.
• Beneficiário: Pablo Vidal Torrado
• Modalidade de apoio: Auxílio à Pesquisa - Regular