IAWA Journal, Vol. 31 (1), 2010: 39–52 WOOD ANATOMICAL FEATURES AND CHEMICAL COMPOSITION OF PROSOPIS KUNTZEI FROM THE PARAGUAYAN CHACO Gunthard Scholz1, Elisabeth Windeisen2, Falk Liebner3, Ernst Bäucker4 and Claus-Thomas Bues4 SUMMARY Anatomical features for Prosopis kuntzei Harms were studied by light and scanning electron microscopy. The wood is mainly diffuse-porous with indistinct growth ring boundaries. Vessel diameter ranges between 11 to 193 µm. The thick-walled fibres average 1275µ m in length. Paren- chyma bands are 66 to 1066 µm apart. Heartwood extractives were studied in the vessels, rays and part of the fibres by means of scanning UV microspectrophotometry. The pyrolitic lignin content is 30.7%. The percentage of polyphenolic compounds, such as flavonoids, hydrolysable tannins and proanthocyanidins, is comparatively high at 5.8%. Total ex- tract contents were determined after organic solvent extractions (23.2%) and water extractions (24.9%). The FTIR spectroscopy showed nearly identical spectra for the methanol and water extracts, with characteristic absorption bands for aromatic substances at 1615 and 1520 cm-1. The spectrum of the acetone extract differs only due to an additional but distinct absorption in the carbonyl range at 1695 cm-1. GC/MS analyses revealed that in the acetone and methanol extracts, tetrahydroxy-flavan- 3-ols (isomers of catechin and epicatechin) were the main constituents with a ratio of 25.3 and 27.6%. Key words: Prosopis kuntzei, wood anatomy, chemical composition. INTRODUCTION The genus Prosopis is one of 78 genera belonging to the subfamiliy Mimosoideae (Evans et al. 2006) and comprises approximately 50 species growing worldwide in tropical and subtropical habitats (Begemann 1966). Prosopis kuntzei Harms occurs in the Chaco region covering parts of Paraguay, Bolivia and Argentina (Dimitri et al. 2000; López 2002). The tree species grows solitarily or in groups (Giménez & Moglia 2003) and is able to colonize abandoned pastures (Dimitri et al. 2000). This is important because the Chaco region – including vast parts of Paraguay, Argentina and Bolivia – is a fragile ecosystem, distinguished by prolongued drought periods and latent water 1) Department of Wood Biology and Wood Technology, Georg-August-Universität Göttingen, Büsgen- weg 4, 37077 Göttingen, Germany. — Corresponding author [E-mail: [email protected]]. 2) Holzforschung München, Technische Universität München, Winzererstraße 45, 80797 München, Germany. 3) Department of Organic Chemistry, University of Natural Resources and Applied Life Sciences, Wien, Austria. 4) Institute for Forest Utilization and Forest Technology, Dresden University of Technology, Pienner Straße 19, 01735 Tharandt, Germany. Downloaded from Brill.com09/24/2021 02:38:59PM via free access 40 IAWA Journal, Vol. 31 (1), 2010 shortage. Intensive land use is characterized by slash and burn, exhaustive cultivation of valuable tree species and adjacent pasture farming. In the Central Paraguayan Chaco alone, 400,000 ha of woodland was legally cleared between the years 2000 and 2003 (Anonymus 2003). The absence of xerophytic forests induces several environmental problems like local salting or devastation of soils. The brownish-violet to dark-blue coloured heartwood possesses good technological properties and is known for its ex- traordinary durability. The tree forms nutritious pods in the dry season which could be used to feed cattle. The tannin content of the pods amounts to approx. 26.6% (Giménez & Moglia 2003) and the protein content to approx. 9% (Scholz et al. 2005). Bees use the tree blossoms to forage for food, making the presence of Prosopis kuntzei important for beekeeping and seed-set in agricultural crops. In literature, the following applica- tions are cited: jewellery, posts (Dimitri et al. 2000), indigenous weapons, charcoal (López 2002), spokes, tool shafts, walking sticks and terrace floors (Giménez & Moglia 2003). According to Scholz et al. (2005), the heartwood is comparable to Bongossi (Lophira alata), especially due to the very high surface hardness. It is suited for ex- terior constructions (e.g., fences, decorative palisades). Furthermore, the timber can be used for tools, musical instruments, sleepers etc. Forestry legislation is insufficient to avoid over-exploitation in these tropical countries. It seems necessary to integrate wood utilization into the agricultural land use. However, for commercial use, extensive information on chemical, structural and physical properties of the wood species must be available. These are the objectives of the present investigation which are, unlike previous literature data, considered for Paraguayan provenances. MATERIALS AND METHODS Material Eight trees from three distinct sites of the Central Paraguayan Chaco were harvested to obtain the raw material. The investigation sites are located 45 km (North-East), 90 km (North-West) and 55 km (South) from the Mennonite settlement Loma Plata (22° 22' 46.55" S, 59° 49' 59.41" W). The tree heights varied between 6–7 m with an average diameter at breast height (dbh) of 29 cm. It was not possible to determine the tree age from tree ring or other analyses. The analysed material was extracted at about 50 cm from the dbh in both directions. Microscopy The brief description of the wood anatomy is based on the definitions of the IAWA List of Microscopic Features for Hardwood Identification (1993), translated and commented on by Richter and Trockenbrodt (1999). Tangential, radial and transverse microscope slides (22–40 µm thick, cut with a sliding microtome), macerated cells and SEM samples (sputter-coated with carbon and gold) of sap- and heartwood were used for anatomical study. Histometric measurements were done from digital images using the software MicroImage (Softwarebürp Weirauch). In addition to anatomical investigations, the chemical composition of crystals was determined by means of SEM energy dispersive X-ray microanalysis (EDX-Röntec M5). Specimens of all eight trees were investigated. Downloaded from Brill.com09/24/2021 02:38:59PM via free access Scholz et al. — Wood of Prosopis kuntzei 41 Topochemical analyses To identify the lignin distribution and other phenolic compounds within the cell walls of Prosopis kuntzei, a heartwood sample (1 × 1 × 5 mm) was transferred to quartz microscope slides for cellular UV microspectrophotometry (Spurr 1969; Koch & Kleist 2001). The sample was analyzed using a Zeiss UMSP 80 microspectrophotometer equipped with a scanning stage which enables the determination of image profiles at constant wavelengths of, e.g., 278 mm. The used scanning software APAMOS® was developed by Zeiss. This program digitizes rectangular fields of the tissue with a lo- cal geometrical resolution of 0.25 × 0.25 µm and a photometrical resolution of 4096 grey-scale levels, which are converted into 14 basic colours to visualize the absorbance intensities. In addition, thin sections were also studied by means of point measurements with a spot size of 1 µm2 between 240 and 560 nm wavelengths in order to characterize the lignin and accessory compounds of phenolic character (Koch & Grünwald 2004). The LAMWIN® computer program was used (ZEISS). One sample was used for the analysis. Wood chemistry Analyses to determine the pH value and ash content (T 211 om-93, 1996) were carried out according to TAPPI (Technical Association of Pulp and Paper Industry) standards. The chemical constitution of Prosopis kuntzei wood samples was studied by means of Curiepoint pyrolysis GC/MS (Roschy et al. 2002; Scholz et al. 2007) using a CPP-40 pyrolyzing unit (FISCHER/GSG) coupled with a GC 6890/MSD 5973 benchtop system (Agilent Technologies). Prior to the analysis, all materials were vacuum-dried and finely ground. Approx. 200µ g of each sample were placed in small FecralloyTM (Goodfellow Ltd.) tubes and subsequently pyrolyzed at 600 °C for 10 seconds The mixture of volatile pyrolysis products was carried into the inlet of the gas chromatograph by helium (250 °C, split 1 : 20). Separation of the various gas com- ponents was achieved using a fused silica column (Optima-5, 30 m, 0.25 mm, 25 µm) with a column flow of 0.9 ml/min, an oven programme starting at 50 °C (5 min) fol- lowed by 5 °C/min to 280 °C (2 min), and an auxiliary temperature of 250 °C. The mass spectrometer was operated in EI mode at 70 eV, 230 °C, and 1.5·10-5 Torr. The total ion chromatograms (programs) were evaluated by using the mass spectra library NIST 2002 (National Institute of Standards and Technology, USA). The pyrolytic lignin and carbohydrate contents of Prosopis kuntzei were calculated from the total peak area of the obtained pyrograms and the total peak area of lignin (LPP) and carbohydrate pyrolysis products (CPP). Sample material of all eight trees was analysed. Quantitative and qualitative determination of the heartwood extractives The heartwood extractives were successively extracted with organic solvents (petro- leum ether, acetone and methanol) using a Soxhlet apparatus according to T 204 om-88 (1996). Further successive extraction was realized with cold and hot water according to T 207 om-93 (1996). Exudates, resulting from bleeding of sap- and heartwood (com- parable with resin exudates) were collected in the field as nuggets of up to a few grams, and analysed. Exudate was not present in all the trees. FTIR spectroscopy was applied Downloaded from Brill.com09/24/2021 02:38:59PM via free access 42 IAWA Journal, Vol. 31 (1), 2010 for the characterisation of extracts and the resin-like exudates. For this purpose, the samples were embedded in KBr pellets (1 mg/300 mg). The FTIR-analyses were car- ried out on a FTS-40 (Biorad) with a resolution of 4 cm-1 (16 scans). The spectra were baseline corrected and normalized at the highest band. GC and GC/MS analyses were carried out after silylation (heating 1 mg sample in 500 µl solvent and 500 µl silylation reagent (Fluka 15239-1) for 1 h at 80 °C), separation and identification were performed on a GC 2010 with FID (Shimadzu) and/or a GC/MS QP 5000 (Shimadzu).