José Carlos Rodrigues

A review of band assignments in near infrared spectra of wood and wood components

Near infrared (NIR) spectra of wood and wood products contain information regarding their chemical composition and molecular structure. Both influence physical properties and performance, however, at present, this information is under-utilised in research and industry. Presently NIR spectroscopy is mainly used following the explorative approach, by which the contents of chemical components and physico–chemical as well as mechanical properties of the samples of interest are determined by applying multivariate statistical methods on the spectral data. Concrete hypotheses or prior knowledge on the chemistry and structure of the sample—exceeding that of reference data—are not necessary to build such multivariate models. However, to understand the underlying chemistry, knowledge on the chemical/functional groups that absorb at distinct wavelengths is indispensable and the assignment of NIR bands is necessary. Band assignment is an interesting and important part of spectroscopy that allows conclusions to be drawn on the chemistry and physico–chemical properties of samples. To summarise current knowledge on this topic, 70 years of NIR band assignment literature for wood and wood components were reviewed. In addition, preliminary results of ongoing investigations that also led to new assignments were included for discussion. Furthermore, some basic considerations on the interactions of NIR radiation with the inhomogeneous, anisotropic and porous structure of wood, and what impact this structure has on information contained in the spectra, are presented. In addition, the influence of common data (pre)-processing methods on the position of NIR bands is discussed. For more conclusive band assignments, it is recommended that wood is separated into its components. However, this approach may lead to misinterpretations when evaluation methods other than direct comparison of spectra are used, because isolation and purification of wood components is difficult and may lead to chemical and structural alterations when compared to the native state. Furthermore, “pure” components have more distinct and symmetric bands that influence the shape of the spectra. This extended review provides the reader with a comprehensive summary of NIR bands, as well as some practical considerations important for the application of NIR to wood.

Determination of lignin content of Eucalyptus globulus wood using FTIR spectroscopy

FTIR spectroscopy was used to quantitatively determine lignin in Eucalyptus globulus wood. A total of 40 wood samples from a 9 year old provenance trial was divided into two independent sets for calibration and validation. Lignin contents, as determined by the acetyl bromide method, ranged from 23 % to 34 % o.d. extractive-free wood. Spectra were recorded with the KBr pellet technique and twelve peaks between 1800cm -1 to 800cm -1 used for calibration by linear regression. The best calibration fit (R 2 =0.98) was obtained with the 1505 cm -1 peak from lignin and the 1157 cm -1 peak from polysaccharides as a reference. The standard error of calibration (SEC), and the standard error of prediction (SEP) calculated with the validation set, were very low. A linear regression of FTIR measurements proved strong enough to predict lignin content with a very high coefficient of determination. The accuracy of FTIR techniques allows its use in large scale breeding programmes to assess wood lignin content with considerable less effort and shorter time than using wet-lab methods, once a reliable calibration is performed for the species.

Genetic parameters of growth and wood quality traits in Picea abies

Genetic parameters were estimated for wood and growth traits in two 19-yr-old clonal trials and a 40-yr-old full-sib progeny trial of Norway spruce [Picea abies (L.) Karst.]. In the clonal trials high (>0.4) broad-sense heritabilities were found for wood density traits, lignin content, number of internal cracks, growth traits, spiral grain and number of resin canals. Moderate (0.2–0.4) heritabilities were found for tracheid lumen diameter and cell wall thickness, microfibril angle and tracheid length, while low heritabilities (<0.2) were found for pulp yield, fibre strength, wood stiffness and wood colour. Lignin content and pulp yield showed low genetic variation, whereas the genotypic coefficient of variation for most other traits ranged between 5 and 15%. Most traits showed low levels of genotype by environment interaction. Among the wood properties, latewood proportion, earlywood density and ring density showed significant, adverse correlations with volume in both clonal trials.

Determination of tree to tree variation in syringyl/guaiacyl ratio of Eucalyptus globulus wood lignin by analytical pyrolysis

Abstract High syringyl/guaiacyl ratios (S/G ratios) are advantageous for pulping. Analytical pyrolysis was applied to Eucalyptus globulus wood to measure S/G ratios and assess its potential in forest breeding programmes. Samples were collected from five trees of two provenances grown in three sites. After peak assignment, relative peak areas were calculated for carbohydrate, guaiacyl and syringyl type degradation products. Lignin derived products account on average for 21% of the total identified area. The average S/G ratio of trees was 2.0, ranging from 1.5 to 2.6. The analysis of variance for the S/G ratios showed that provenance and tree were highly significant sources of variation accounting for 48 and 27% of the variation, respectively. Site had no influence but ‘site×provenance’ interaction was significant and accounted for 16% of the variation. The error associated with the method represented only 6% of the variation. Analytical pyrolysis proved reproducible and sensitive for the measurement of the natural variability of E. globulus with regard to lignin composition. The pyrolytic determination of the S/G ratios is recommended as an evaluation trait in breeding programmes for pulpwood production.

Calibration of NIR to assess lignin composition (H/G ratio) in maritime pine wood using analytical pyrolysis as the reference method

-hydroxyphenyl (H), guaiacyl (G) and, if detectable(Saito et al. 2005), negligible (Obst and Landucci 1986)amounts of syringyl (S) phenylpropanoid units. Theimportance of lignin composition in terms of H/G ratio insoftwoods for the pulping industry has led to attemptsat genetic modification (MacKay et al. 1999; Wadenba¨cket al. 2004). Nevertheless, very little is known about thenatural variation of lignin composition. The lack of a suit-able method to assess lignin composition in a largenumber of samples can in part explain this situation.Ana-lytical pyrolysis is being increasingly used to assesslignincomposition (Obst and Landucci 1986; Faix et al. 1993;Choi et al. 2001; Rodrigues et al. 2001; Yokoi et al. 2001;Kuroda et al. 2002; del Rio et al. 2005; Meier et al. 2005)but even if time requirements for the analyticalprocedureare well below those involved in wet-chemical analysis(Meier and Faix 1992) it is still demanding when largescreening programs are necessary.The simplicity, rapidity, and high reproducibilityofnear-infrared spectroscopy (NIRS) have widened its use tothe determination of the chemical composition of ligno-cellulosic materials as a substitute for wet-chemistrytechniques (Schwanninger and Hinterstoisser 2001; Gier-linger et al. 2002; Raymond and Schimleck 2002; Schim-leck et al. 2003).The aim of this work was to use analytical pyrolysisdata to develop an NIR method for determining H/Gratios, with a focus on assessment of the naturalvariationof lignin composition in maritime pine wood.

Influence of tree eccentric growth on syringyl/guaiacyl ratio in Eucalyptus globulus wood lignin assessed by analytical pyrolysis

Abstract Wood disks from 9-year-old Eucalyptus globulus trees that showed eccentric growth were analysed by analytical pyrolysis to determine lignin syringyl/guaiacyl (s/g) ratio, lignin content and polysaccharide composition (hexosans/hexosans+pentosans). Three cross-sectional fractions were analysed: the long radius, the short radius and the intermediate sections. Between-tree variation was observed for the s/g ratio from 2.0 to 2.8, the lignin content from 26.5 to 28.0% and the hesosans/hexosans+pentosans ratio from 0.76 to 0.83. The reliability of the pyrolysis analysis assessed by the pooled standard deviation was very high for the three determinations (2–3% coefficients of variation). Eccentric tree growth in E. globulus has no impact in the s/g ratio and does not necessarily imply differences in lignin content or in polysaccharide composition. When differences occur, lower lignin and higher cellulose are found in the cross section part with the highest radial growth. Sampling for wood chemical analysis in eccentric cross sections should avoid the stem parts with high radial differences between opposite sides. Analytical pyrolysis can be used to prospect for the presence of tension wood.

Genetic Variation in the Chemical Components of Eucalyptus globulus Wood

Despite the ecological and economic importance of lignin and other wood chemical components, there are few studies of the natural genetic variation that exists within plant species and its adaptive significance. We used models developed from near infra-red spectroscopy to study natural genetic variation in lignin content and monomer composition (syringyl-to-guaiacyl ratio [S/G]) as well as cellulose and extractives content, using a 16-year-old field trial of an Australian tree species, Eucalyptus globulus. We sampled 2163 progenies of 467 native trees from throughout the native geographic range of the species. The narrow-sense heritability of wood chemical traits (0.25–0.44) was higher than that of growth (0.15), but less than wood density (0.51). All wood chemical traits exhibited significant broad-scale genetic differentiation (QST = 0.34–0.43) across the species range. This differentiation exceeded that detected with putatively neutral microsatellite markers (FST = 0.09), arguing that diversifying selection has shaped population differentiation in wood chemistry. There were significant genetic correlations among these wood chemical traits at the population and additive genetic levels. However, population differentiation in the S/G ratio of lignin in particular was positively correlated with latitude (R2 = 76%), which may be driven by either adaptation to climate or associated biotic factors.

QTLs and candidate genes for wood properties in maritime pine (Pinus pinaster Ait.)

A three-generation outbred pedigree of 186 individuals was used to identify the genomic regions involved in the variability of chemical and physical wood properties of Pinus pinaster. A total of 54 quantitative trait loci (QTLs) was detected, with an average of 2.4 QTLs per trait. Clusters of wood properties QTLs were found at several points in the genome, suggesting the existence of pleiotropic effects of a limited number of genes. The co-localizations observed in this study are in accordance with the genetic correlations previously reported in the literature. In addition, in an attempt to identify the genes underlying the QTLs, nine wood quality candidate genes involved in cell wall structure were localized on the genetic map. Only one of them, Korrigan, a gene encoding for a β 1-4 endo-glucanase known in Arabidopis thaliana to be involved in polysaccharide biosynthesis, co-localized with a wood quality QTL cluster involved in hemicellulose content and fibre characteristics. This finding is in accordance with results previously reported for this gene regarding its expression variability (transcriptome and proteome levels) and patterns of molecular evolution. The pertinence of this result will be tested in more rigorous designs in order to identify early selection predictors for wood quality.

Molecular and phenotypic profiling from the base to the crown in maritime pine wood‐forming tissue

Environmental, developmental and genetic factors affect variation in wood properties at the chemical, anatomical and physical levels. Here, the phenotypic variation observed along the tree stem was explored and the hypothesis tested that this variation could be the result of the differential expression of genes/proteins during wood formation. Differentiating xylem samples of maritime pine (Pinus pinaster) were collected from the top (crown wood, CW) to the bottom (base wood, BW) of adult trees. These samples were characterized by Fourier transform infrared spectroscopy (FTIR) and analytical pyrolysis. Two main groups of samples, corresponding to CW and BW, could be distinguished from cell wall chemical composition. A genomic approach, combining large-scale production of expressed sequence tags (ESTs), gene expression profiling and quantitative proteomics analysis, allowed identification of 262 unigenes (out of 3512) and 231 proteins (out of 1372 spots) that were differentially expressed along the stem. A good relationship was found between functional categories from transcriptomic and proteomic data. A good fit between the molecular mechanisms involved in CW-BW formation and these two types of wood phenotypic differences was also observed. This work provides a list of candidate genes for wood properties that will be tested in forward genetics.

Plasticity of maritime pine (Pinus pinaster) wood‐forming tissues during a growing season

The seasonal effect is the most significant external source of variation affecting vascular cambial activity and the development of newly divided cells, and hence wood properties. Here, the effect of edapho-climatic conditions on the phenotypic and molecular plasticity of differentiating secondary xylem during a growing season was investigated. Wood-forming tissues of maritime pine (Pinus pinaster) were collected from the beginning to the end of the growing season in 2003. Data from examination of fibre morphology, Fourier-transform infrared spectroscopy (FTIR), analytical pyrolysis, and gas chromatography/mass spectrometry (GC/MS) were combined to characterize the samples. Strong variation was observed in response to changes in edapho-climatic conditions. A genomic approach was used to identify genes differentially expressed during this growing season. Out of 3512 studied genes, 19% showed a significant seasonal effect. These genes were clustered into five distinct groups, the largest two representing genes over-expressed in the early- or late-wood-forming tissues, respectively. The other three clusters were characterized by responses to specific edapho-climatic conditions. This work provides new insights into the plasticity of the molecular machinery involved in wood formation, and reveals candidate genes potentially responsible for the phenotypic differences found between early- and late-wood.