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Previous issue date: 2015-02-25 === CAPES === According to the Brazilian Soil Classification System the Organossolos (Histosols) are characterized by horizons with high organic matter content and a given thickness. The carbon content is related to pedogenesis processes; however for the carbon addition and maintenance in the soil in such amount and thickness to meet the criteria of the classification system there are several factors working in conjunction, culminating in the soil genesis process. These soils can be formed by paludization or litter accumulation. The overall objective of the study was to characterize and classify Organossolos and to verify the influence of their genesis in the soil attributes, evaluating physical and chemical properties; in addition, the application of isotopic methods for analyzing natural abundance of carbon and nitrogen isotopes, relating the data with changes in vegetation and in soil evolution. The soils are under Atlantic Forest in the state of Rio de Janeiro. There were selected four profiles in different environments, one in the municipality of Mag? in the plains neighboring the Guanabara Bay, the second in Campos dos Goytacazes municipality, near Lagoa Feia, both in hot and humid climate and lowland plain relief. Two other soil profiles were located in Itatiaia municipality, in the highland section of the Itatiaia National Park, under cold weather and humid and mountainous vegetation environment. A series of analytical procedures were made: description and morphological characterization, analysis of chemical and physical properties, determination of carbon and nitrogen, chemical fractionation of humic substances, mineral material (MM), density of organic matter (DOM), minimum residue (MR), solubility in sodium pyrophosphate (SSP), determination of fibers and Von Post decomposition scale; plus the quantification of natural abundance of carbon isotopes (12C and13C) and nitrogen (14N and 15N), and carbon dating by the method of C. The RJ-01 profile was classified as ORGANOSSOLO Tiom?rfico S?prico t?pico, the RJ-02 as ORGANOSSOLO H?plico S?prico t?pico, the RJ-03 as ORGANOSSOLO H?plico H?mico t?pico and RJ-04 as ORGANOSSOLO F?lico S?prico cambiss?lico, equivalent to Sulfosaprists (RJ-01) Haplosaprists (RJ-02), Haplohemists (RJ-03) and Udifolists (RJ-04), in the Soil Taxonomy (USDA-NRCS). The RJ- 01 was significantly thicker and higher in carbon content in the subsurface. The RJ-02 profile was shallower, but had a higher organic matter deposition. The RJ-03 profile had the organic matter (OM) with the oldest C dating, in the range of 3351-3699 years at 40-50 cm. However, the RJ-04 profile stood out from the others because it had better soil drainage, higher degree of OM humification. Also, this profile had a variation of ?6 of 13C, indicating a change in local floristic composition with an increase of vegetation with C3 photosynthetic cycle, which is a hint of climate change. === De acordo com o Sistema Brasileiro de Classifica??o de Solo os Organossolos s?o caracterizados por horizontes com elevado teor de material org?nico e uma espessura m?nima. O teor de carbono esta ligado ao processo pedogen?tico, por?m para que ocorra a adi??o e manuten??o de carbono em quantidade e espessura de forma a atender os crit?rios do sistema de classifica??o uma s?rie de fatores atua em conjunto, culminando com o processo de g?nese do solo. Esses solos podem ser formados atrav?s de um desses processos: paludiza??o ou acumula??o de liteira. O objetivo geral do trabalho foi caracterizar e classificar Organossolos e verificar a influ?ncia da sua g?nese sobre os atributos ed?ficos, analisando as propriedades f?sicas e qu?micas; ainda a aplica??o de m?todos de an?lise da abund?ncia natural de is?topos de carbono e nitrog?nio, relacionando-as as altera??es na vegeta??o e na evolu??o do solo, em dois ambientes de Floresta Atl?ntica, no Estado do Rio de Janeiro. Para tanto foram selecionados quatro perfis em locais distintos, um em Mag? ao fundo da Ba?a de Guanabara, o segundo em Campos dos Goytacazes pr?ximo a Lagoa Feia, ambos em ambientes de clima quente e ?mido e relevo plano de v?rzea. Outros dois perfis localizam-se em Itatiaia, na parte alta do Parque Nacional de Itatiaia (PNI), em ambiente de clima frio e ?mido e vegeta??o altomontana. Realizou-se uma s?rie de procedimentos anal?ticos: descri??o e caracteriza??o morfol?gica, an?lises de atributos qu?micos e f?sicos, determina??o de carbono e nitrog?nio, fracionamento qu?mico das subst?ncias h?micas, material mineral (MM), densidade da mat?ria org?nica (DMO), res?duo m?nimo (RM), solubilidade em pirofosfato de s?dio (IP), determina??o de fibras (FE e FN) e escala de decomposi??o de Von Post, abundancia natural de is?topos do carbono (12C e 13C) e nitrog?nio (14N e 15N) e data??o da mat?ria org?nica do solo atrav?s do m?todo de C. O perfil RJ-01 foi classificado como ORGANOSSOLO Tiom?rfico S?prico t?pico, o RJ-02 como ORGANOSSOLO H?plico S?prico t?pico, o RJ-03 como ORGANOSSOLO H?plico H?mico t?pico e o RJ-04 como ORGANOSSOLO F?lico S?prico cambiss?lico. O perfil RJ-01 apresentou maior espessura e teores de carbono mais elevados em subsuperf?cie. O perfil RJ-02 foi o de menor profundidade, por?m possui maior deposi??o atual de mat?ria org?nica (MO). O perfil RJ- 03 possui a MO mais antiga, datando na faixa de 3351-3699 anos a 40-50 cm. No entanto, o perfil RJ-04 destacou-se dos demais por apresentar melhor drenagem e maior grau de humifica??o da MO. Al?m disso, esse perfil mostrou varia??o do valor de C de ?6, indicando altera??o na composi??o flor?stica local, com o aumento de vegeta??o do ciclo fotossint?tico C3, o que ? apontado como ind?cio de altera??es clim?ticas.
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