WOOD STRUCTURE and Topochemistry of Juniperus Excelsa

IAWA Journal, Vol. 32 (1), 2011: 67–76 WOOD STRUCTURE AND toPOCHEMISTRY OF JUNIPERUS EXCELSA Stergios Adamopoulos1* and Gerald Koch2 SUMMARY Wood structure and topochemical distribution of lignin and phenolic extractives in Juniperus excelsa Bieb. were investigated using a mature specimen, aproximately 80 years of age, from the Rhodope mountains, Greece. The wood of J. excelsa was found to possess the same qualita- tive anatomical features as those reported for other Juniperus species of the Western Hemisphere. Quantitative anatomical characteristics recorded for mature wood (heartwood and sapwood) included earlywood and latewood tracheid length, double wall thickness of earlywood and latewood tracheids, lumen diameter of earlywood tracheids and ray height. Scanning UV microspectrophotometry revealed a pronounced lignification of J. excelsa tracheids with detected absorbance values of the secondary cell wall layers being much higher in comparison to all other softwoods studied using this technique. The cell corners and com- pound middle lamellae were characterised by relative high UV absorbance values as compared to the S2 layers. The phenolic compounds deposited in the axial and ray parenchyma cells possessed higher absorbance values than cell wall associated lignins and had a different spectral be- haviour due to the presence of chromophoric groups. According to the obtained UV absorbance spectra, more condensed phenolic compounds were deposited in the heartwood than in the sapwood. Key words: Juniperus excelsa Bieb., wood anatomy, scanning UV microspectrophotometry, lignin distribution, phenolic extractives. INTRODUCTION Juniperus (Cupressaceae) is the second largest genus of the conifers and consists of approximately 60 species distributed almost exclusively in the Northern Hemisphere. Because of its site-insensitivity and ability to grow on shallow and stony soils in severe environments the genus is extremely diverse with species forming prostrate mats above the timberline, to large trees up to 50–60 m in height nearer to sea level (Florin 1963). 1) Technological Educational Institute of Larissa, Department of Forestry and Management of Natu- ral Environment, 43100 Karditsa, Greece. 2) Institute for Wood Technology and Wood Biology, Federal Research Institute of Rural Areas, Forestry and Fisheries (vTI), Leuschnerstr. 91, 21031 Hamburg, Germany. *) Corresponding author [E-mail: [email protected]]. Associate Editor: Alex Wiedenhoeft Downloaded from Brill.com09/24/2021 06:19:30PM via free access 68 IAWA Journal, Vol. 32 (1), 2011 Juniperus excelsa Bieb. extends from the central and south Balkans through Ana- tolia to Crimea, central and southwest Asia and east Africa (Boratynsky et al. 1992; Christensen 1997). Juniperus excelsa creates extended forests in Balouchistan of Pakistan and in Turkey. Moreover, it is the dominant woody plant species above 2,100 m altitude in almost all the northern mountains of Oman (Ahmed et al. 1990; Gardner & Fisher 1996; Carus 2004). It is considered a slow growing species and can attain a height of 20 m (Ahmed et al. 1990). In Greece, the species is commonly found on rocky regions at altitudes of 50 to 1,600 m as a component of degraded shrublands, as scattered individual trees or as small groups of trees in open forests and rarely as larger units of mixed or pure stands (Athanasiadis 1986). Because of the high natural durability of the heartwood, dimensional stability, good machinability, and moderate strength as well as decorative colour and texture, J. excelsa timber is highly desirable for furniture, building components, flooring, and poles (Tsoumis 1991). Successive intense anthropogenic disturbances, grazing, and illegal cuttings have led to the degradations of J. excelsa old-growth stands and have limited the availability of large-diameter timbers (Milios et al. 2007). Therefore, nowadays its wood is mainly used for turnery, carvings, novelties and small agricultural construc- tions. The wood anatomy and chemistry of J. excelsa has not been studied in detail, un- like many Juniperus in the Western Hemisphere (Phillips 1968; Herbst 1978; Panshin & deZeeuw 1980; ter Welle & Adams 1998; Bauch et al. 2004). Recently, degraded J. excelsa stands in northeast Greece have received attention in terms of their growth ecology, structure, and regeneration patterns (Milios et al. 2007, 2009) while utilisation potentials might also arise. A better insight of J. excelsa wood anatomy and chemistry at the cell wall level could serve as a basis for understanding its wood properties and improve the wise use of its timber. The present study reports the wood anatomical characteristics and scanning UV microspectrophotometric analyses on the distribution of lignin and phenolic extractives in the heartwood and sapwood of J. excelsa. MaterialS AND METHODS The study material originates from Juniperus excelsa stands located in moderate most south facing slopes of the Pascalia public forest (41° 11'–41° 15' N, 24° 33'–24° 41' E). The forest lies in the central part of the Nestos valley at the Rhodope mountains, Greece. The elevation ranges from 100 to 350 m. The annual rainfall of the area is 676 mm and the mean yearly temperature is 13.4 °C. The substrate is limestone and the soils are sandy-clay and rocky. A cross-cut, with mean diameter 20.1 cm, was taken at breast height from a dominant tree approximately 80 years of age and 7.9 m in height to carry out wood anatomical and topochemical studies. The mean diameter of heartwood was 7.0 cm while the mean width of sapwood 10.1 cm. Our tree was a healthy mature individual, representative of J. excelsa stands in the area. Moreover, it was selected among other trees with minimal lean as to avoid compression wood. The cross-cut at breast height did not show any marked eccentric growth. Downloaded from Brill.com09/24/2021 06:19:30PM via free access Adamopoulos & Koch — Topochemistry of Juniperus wood 69 Light microscopy Transverse, radial, and tangential sections (15–20 µm thick) were sequentially pre- pared from cambium to pith using a sliding microtome. Several sections of heartwood and sapwood were both unstained and double stained with safranin and astra blue, and embedded with Euparal for normal light microscopy. Furthermore, wood material was reduced to slivers separately for heartwood and sapwood and macerated in a mixture of equal parts of acetic acid and hydrogen peroxide (20 vol) in an oven at 60 °C for 48 hours (Tsoumis 1991). The macerations were mounted in glycerine for tracheid length measurements. We selected five successive growth rings with moderate width in each of three radial positions for determining tracheid length values in heartwood and sapwood. Heartwood material was taken more peripheral than ring 25 to avoid juvenile wood, at approximately 2.5 cm from the pith. Sapwood being wider than heartwood was sampled at approximately 5.5 cm and 8.5 cm from the pith. Microscopic observations and analysis were carried out with an Olympus AX 70 microscope and a digitized image analysis system (analySIS®, Olympus). Descriptive terminology followed the IAWA List of Microscopic Features for Softwood Identifica- tion (IAWA Committee 2004). About 100 measurements for tracheid length and 50 measurements for all other microscopic features (cell wall thickness, lumen diameter) were taken (Hapla & Saborowski 1987). Cell wall thickness and lumen diameter were measured in the tangential direction. Ultra-violet (UV) microspectrophotometry (UMSP) The topochemical distribution of lignin and phenolic extractives was investigated on a subcellular level using scanning UV microspectrophotometry (Zeiss UMSP 80 microspectrophotometer) as in Koch and Kleist (2001) and Koch and Grünwald (2004). Small heartwood and sapwood blocks (1 × 1 × 5 mm) were directly embedded in Spurr’s epoxy resin (Spurr 1969) under mild vacuum with several cycles of evacuation and ventilation as described by Kleist and Schmitt (1999) to avoid chemical changes of the extractives caused by reactions with solvents. Transverse sections of 1 µm in thickness were cut with an ultramicrotome equipped with a diamond knife. The sections were transferred to quartz microscope slides, embedded in non-UV absorbing glycerine and covered with a quartz cover slip. The topochemical analyses were carried out with a UMSP 80 microspectrophotometer (Zeiss) equipped with a scanning stage which enables the determination of image profiles at defined wavelengths with the scan softwareAPAM OS® (Zeiss). The topochemical distribution of lignin and extractives was recorded at a defined wave- length of 280 nm (representing the absorbance maximum for softwood lignin). The scan program digitises rectangular fields on the tissue with a local geometrical resolution of 0.25 × 0.25 µm and a photometrical scale resolution of 4096 grey scale level, which are converted to 14 basic colours to visualize the UV absorbance intensities. The scans were depicted as two-dimensional image profiles, including a statistical evaluation of the UV absorbance values. The photometric characterisation of individual cell wall layers and tissues impreg- nated with extractives was additionally carried out by point measurements with a Downloaded from Brill.com09/24/2021 06:19:30PM via free access 70 IAWA Journal, Vol. 32 (1), 2011 spot size of 1 µm2 between 240 and 560 nm wavelengths. For quantitative studies, 15 spectra were taken from each cell wall layer and cell type, respectively and evaluated with the program LAMWIN® (Zeiss). The

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