Termodecomposição, estudos de carbonização e silicificação da matéria orgânica e corpos silicosos em ecossistemas terrestres no Brasil e na Antártica / Thermodecomposition, organic matter carbonization silicification studies and silica bodies in terrestrial ecosystems in Brazil and Antarctica

AUTOR(ES)

Roseilton Fernandes dos Santos

DATA DE PUBLICAÇÃO

2007

RESUMO

Soil organic matter (SOM) is highly heterogeneous in composition, which consists of components as different from each other as labile carbohydrates and recalcitrant aliphatic compounds. Mean residence time (MRT) of the various compounds comprising soil organic matter may range from a few minutes to thousands of years. This wide range is partly due to the soil predominant clay mineral type, which may influence SOM dynamics and interaction with the mineral fraction. Soil organic matter building occur through the synthesis of organic compounds in photosynthesis and depends on soil and climatic conditions. The loss of SOM as CO2 depends on physical, chemical and biological processes which control soil carbon cycle. There are scarce studies on the effects of temperature variation on soil organic matter decomposition, although such studies would provide a better understanding of OM nature in natural systems, including those which undergo natural or man-made fires. The soil samples (n=11) selected for this study are representative of different ecosystems, and were chosen because of the ecological peculiarities of each area as well as because of the varying humification pathways which take place in those areas. The aims of this work were: a) to understand how soil organic matters behaves after heat treatments and how its stability is influenced by soil chemical, physical and mineralogical characteristics; b) proceed the chemical and mineralogical characterization fossilized carbon in petrified wood fragments from Antarctica; c) identify silica phytoliths in superficial horizons of soils from different terrestrial ecosystems. OM stability based on thermogravimetric data showed that clayey Latosols possess the most stable carbon forms. Thermodecomposition showed decreasing OM values towards Caratinga-Berilo-Crato, which follows a decreasin latitude gradient, from Southeast to Northeast. Fiber content increase in Organosols enhanced thermodecomposition resistence. The mineral carbon polymorph in fossilized wood fragments in graphite. Besides graphite, mineral matrix of the petrified material is constituted by quartz by other mineral or minerals, poorly crystalline, which are relatively rich in Fe, Al, and MG and not detected by X-ray crystallography. There occurs a natural abundance in phytoliths and phytolith morphotypes in studied soils: variously sized rods, saddles, fan-shaped, dumbells and rectangular shapes, with rods and fans the most abundant. Silica bodies were more abundant and diversified in the only soil developed on quartzite, naturally rich in silica and with a vegetation which accumulates silicon.

ASSUNTO(S)

solo soil organic matter fitólitos graphite grafite matéria orgânica silica phytoliths ciencia do solo

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