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Title: Uso de aminoácidos como indicadores de deposição e fonte da matéria orgânica em manguezal
Keywords: Degradação de matéria orgânica;  Manguezal;  Aminoácido;  Índice de reatividade;  Amino acids;  Organic matter;  Reactivity index;  Mangrove
Issue Date: 1-Jan-2008
Abstract: This work was realized in Bragança's peninsula, in the North of Brazil, where a transect with 14 points, containing different vegetation types and flood regimes, was chosen for the collection of cores. In these cores were analyzed total nitrogen (NT) and total organic carbon (TOC) in order to obtain a general characterization of the organic matter (MO). The isotopes 15N and 13C were analyzed to trace sources of organic matter and as indicators of saline stress. The total hydrolysable amino acids (THAA) were determinate to obtain the degradation index (ID) in sediments with different vegetations, in the surface and in the sedimentary column. The isomers of amino acids (enantiomers D and L) were determinates to markers the microbial transformation. The variation of NT, TOC, 15N, 13C and THAA characterized the organic matter in two groups: the first under the surface is strongly influenced by the vegetation and the second in the column of sediment is mainly influenced by decomposers bacteria action. The superficial variation was influenced mainly by the vegetation. This is clear in the points 1 to 7, where the vegetation of Sesuvium portulacastrum was responsible for high values of TN and TOC, in comparison to the points 8 to 14 with vegetation of Avicennia germinans. The ID found for the superficial variation divides the MO in 3 subgroups, the first (points 1 to 4) with less degraded MO, in comparison to second (points 5 to 9) and the third (points 10 to 13) groups. The correlations between C/N, ratio glutamine/acid -aminobutiric (Glu / - aba) and ratio asparagine/ß-alanine (Asp/ß-ala) (R=-0,83 and R=-0,89, n=62, respectively) demonstrate that the bacterial action under point 1 to 7 it is smaller than in the points 8 to 14, resulting in a MO more degraded in the points 8 to 14. In the sedimentary column the most abundant amino acids were glycina, aspartic acid, alanine and glutamic acid. Through a cluster analysis the amino acids were divided in two groups, the first composed of threonine, alanine, tyrosine, valine, isoleucine, leucine, phenylalanine and histidine and the second is composed of asparagine, glutamine, serine and glycine. In the variation of ID in all points and depths, it was seen a decrease between the surface and depths, what does indicate that the MO in the surface is less degraded and labil that the MO in the sedimentary column. This is supported by the negative correlations among ID with Asp/ß-ala, Glu/ -aba and glucosamine/galactosamine (glc-NH2/gal-NH2, R=-0,89, R=-0,72 and R=-0,81, n=182, respectively) that demonstrate that ID in the sedimentary column is affected mainly by the bacterial action. The variation of THAA in TOC (THAA-C) and THAA in NT (THAA-N), on the dated cores (points 1, 9 and 14) do identifies the decrease of the marine influence in two dry periods (the first between 2000 years BP and 1000 years BP and the second between 400 years BP and the present time). The increase of the D-amino acids with the depth as well as the ratio glc-NH2/gal-NH2 confirms the increase of the bacterial action with the depth, what makes the MO more refractory. Therefore the ID for this data set is an efficient way to determine the degree of degradation of MO.
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