Composição isotópica estável de carbono e nitrogênio do lenho de Dinizia excelsa Ducke (Fabaceae)

Abstract

Verifying the true origin of wood is a fundamental step in combating illegal timber trade. A promising method for determining the origin of wood consists of the use of stable isotopes, but there is a lack of studies that investigate the stable isotopic composition of wood species of interest, aiming to provide support for the application of this method to combat illegal trade in this resource. This work has the general objective of investigating the variation in the isotopic composition of δ15N and δ13C of the wood of an Amazonian tree species of great commercial value (Dinizia excelsa – angelim-vermelho) in pristine forests of the Brazilian Amazon aiming to: (i) characterize the variation in the ratios isotopic compositions of the elements 15N and 13C along the radial diameter of the stem and (ii) evaluate whether the variation in the isotopic composition of δ15N and δ13C of the wood of different D. excelsa is dependent on the sampling sites, for the purpose of determining the origin of the material . To this end, this work was divided into two chapters whose methods and results will be summarized separately below: 1. to analyze the radial variation in the isotopic ratios of δ15N and δ13C in the wood of D. excelsa, a disk was sampled in eight different positions in the radial direction, using a portable drill with a 5 mm drill bit. Seven samples were extracted from each position, totaling 56 flaked wood samples. The samples were treated and analyzed in an elemental analyzer coupled to an isotope ratio mass spectrometer (IRMS) to determine the concentration of elements 13C and 15N. In general, the absolute values of δ15N varied between -0.54 and 1.60‰, and those of δ13C between -27.88 and -26.55‰, in which δ15N showed greater variation between positions. It was observed that the sampling position influences the isotopic values of δ15N and δ13C, as well as, there is a greater variation of δ15N and δ13C in the regions closest to the pith and peel. Despite this variation, samples taken from the heartwood region can guarantee more homogeneous data. 2. to investigate the variation in the composition of δ15N and δ13C isotopes depending on the origin of the samples, the isotopic composition of δ15N and δ13C of the wood of 34 trees from four sites distributed in the Brazilian Amazon was quantified. The results indicated greater variation in the δ15N isotope compared to the δ13C isotope in tree wood, with this variation depending on the site studied. Regarding the separation of sites based on the isotopic ratios of δ15N and δ13C, a successful separation was observed between the site located in the Eastern Amazon (Juruti) and the sites in the Central Amazon (Silves and Itapiranga). However, the territorially closest sites (Silves and Itapiranga) presented more homogeneous values, resulting in overlapping of isotopic values in the analyzes and limited separation. Therefore, there is a high potential for δ15N results to define the origin of the sampled material. These results show that, although the sampling position influences the δ15N and δ13C values, samples taken from the heartwood region can guarantee more homogeneous isotopic data. It is also concluded that the variation in the isotopic ratios of δ15N and δ13C are dependent on the sampling site, as well as the δ15N isotope has potential as an indicator of the origin of wood. Such discoveries contribute to the understanding of the variation in the stable isotopic composition of tropical wood, and can provide information for refining forensic wood tracking methods.