Abstract
The anatomical characteristics and the physical and chemical properties of wood of Quercus macdougallii Martínez are presented for the first time. Q. macdougallii Martínez is an endemic species of the Sierra Juarez of Oaxaca. The microscopic characteristics were described in preparations of typical cuts and dissociated material. The physical properties were evaluated according to the ASTM D 143-94 standard in sapwood and heartwood specimens. The measurable elements and physical properties were classified according to the mean. With the measurable elements, the paper pulp quality index was determined. In sapwood and heartwood, the basic chemical composition was determined. The wood of Q. macdougallii presented a pronounced grain, a thick texture, and a straight thread. Fibers, fibrotracheids, uniseriate, multiseriate, and aggregate rays were found. Basic density 0.55 g cm-3 in sapwood and 0.61 g cm-3 in heartwood is classified as moderately heavy and heavy, respectively. The saturation point of the fiber is classified as high. Based on its physical properties, Q. macdougallii wood can be used in the manufacture of furniture, veneer, floors, tool handles, and construction. Based on the pulp quality indices and chemical composition, this wood could be used to obtain cellulose pulp for paper.
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Anatomical Characterization, Physical, and Chemical Properties of Wood of Quercus macdougallii Martínez, Endemic Species of the Sierra Juárez of Oaxaca, Mexico
Faustino Ruiz-Aquino,a Lizbeth Luna-Bautista,a Aremi E. Luna-Bautista,a Wenceslao Santiago-García,a Luis F. Pintor-Ibarra,b and José G. Rutiaga-Quiñones b,*
The anatomical characteristics and the physical and chemical properties of wood of Quercus macdougallii Martínez are presented for the first time. Q. macdougallii Martínez is an endemic species of the Sierra Juarez of Oaxaca. The microscopic characteristics were described in preparations of typical cuts and dissociated material. The physical properties were evaluated according to the ASTM D 143-94 standard in sapwood and heartwood specimens. The measurable elements and physical properties were classified according to the mean. With the measurable elements, the paper pulp quality index was determined. In sapwood and heartwood, the basic chemical composition was determined. The wood of Q. macdougallii presented a pronounced grain, a thick texture, and a straight thread. Fibers, fibrotracheids, uniseriate, multiseriate, and aggregate rays were found. Basic density 0.55 g cm-3 in sapwood and 0.61 g cm-3 in heartwood is classified as moderately heavy and heavy, respectively. The saturation point of the fiber is classified as high. Based on its physical properties, Q. macdougallii wood can be used in the manufacture of furniture, veneer, floors, tool handles, and construction. Based on the pulp quality indices and chemical composition, this wood could be used to obtain cellulose pulp for paper.
Keywords: Sapwood; Wood basic density; Pulp quality indexes; Wood chemistry
Contact information: a: Instituto de Estudios Ambientales, Universidad de la Sierra Juárez, Avenida Universidad S/N, , Ixtlán de Juárez, Oaxaca, C.P. 68725 México; b: Facultad de Ingeniería en Tecnología de la Madera, Edificio “D”, Ciudad Universitaria, Universidad Michoacana de San Nicolás de Hidalgo, Av. Fco. J. Múgica S/N, Col. Felicitas del Rio, Morelia, Michoacán, C. P. 58040, México;
* Corresponding author: rutiaga@umich.mx
INTRODUCTION
Oaks belong to the genus Quercus in the family Fagaceae, which comprises 8 to 10 genera and more than 900 species (Kremer et al. 2012). The genus Quercus is distributed throughout Mexico with 161 registered species. The states with the highest number of species are Oaxaca (48), Nuevo León (47), Jalisco (45), Chihuahua (40), and Veracruz (38) (Valencia and Nixon 2004).
The Sierra Norte in the state of Oaxaca has the highest species diversity with 23 of the total registered. Quercus macdougallii Martínez, the endemic species of the Sierra de Juárez in Oaxaca, is distributed in this region due to its reduced geographical and altitudinal distribution (Valencia and Nixon 2004).
Quercus macdougallii is a monoecious evergreen tree that can grow up to 40 m high, and the stem diameter can reach 4 m as an adult. Additionally, its flowering period is from May to July and it bears fruit from November to January (Clark-Tapia et al. 2018). It is distributed within the mountainous system called Sierra Madre de Oaxaca, specifically in the municipalities of San Pedro Yólox and Santiago Comaltepec. The area includes a mountain range with different elevations from 2648 to 3274 m above sea level (Anacleto-Carmona 2015).
Studies related to Q. macdougallii have been limited to tree structure and diversity (Anacleto-Carmona 2015), acorns sexual reproduction (Clark-Tapia et al. 2018), the effect of magnetite nanoparticles on the germination, early growth of Q. macdougallii (Pariona et al. 2017), and the delimitation of the climatic intervals where the maximum abundance of the species occurs (Antúnez et al. 2018).
The distribution of Q. macdougallii is restricted, with low abundance. Clark-Tapia et al. (2018) found sites with 150 trees per hectare, while Antúnez et al. (2018), report the presence of the species in 33 sites of 1000 m2. However, information related to the characteristics of its wood was lacking. Therefore, the aim of this study was to perform the macroscopic and microscopic anatomical description of the wood. Additionally, the study evaluated the physical properties at different heights of the stem, and the chemical composition, as a contribution to the technological knowledge of the wood in this species.
EXPERIMENTAL
Materials
Study area
The study area was in the forests of the community of Santiago Comaltepec in the Sierra Norte of Oaxaca, at coordinates 17°33′ 50” LN and 96° 32′ 52” LO with altitude levels ranging from 450 to 3,000 m (INEGI 2016). The climate in this zone is temperate with low temperatures from November to February (minimum average 4.7 °C) and high temperatures from March to May (maximum average 13.4 °C) (Robson 2008; Antúnez et al. 2018). The average rainfall is 767 mm (Clark-Tapia et al. 2016). The collection site is located at coordinates 07°64’129″ LN and 19°45’810″ LO at an altitude of 2936 m.
Tree selection
A Q. macdougallii tree was studied that was knocked down by the wind. The tree showed straightness of stem and was free of pests or diseases. The tree had a diameter of 28 cm at breast height and a total height of 13 m. Dimensioning was done according to the methodology of Ramos and Diaz (1981). Logs of 40 cm in length were cut at different heights above ground level (0.30 m, 1.30 m, 3 m, and 6 m). A botanical sample was collected and identified in the herbarium of the University of Sierra Juarez. Based on the availability of the study material, it was only possible to describe the wood with one individual (De la Paz Pérez and Quintanar 1994; Bárcenas et al. 2005; De la Paz Pérez and Dávalos-Sotelo 2008). However, the values obtained for some physical properties should be considered with some caution.
Methods
Macroscopic and microscopic anatomical characterization
For the macroscopic description, a 30-cm thick slice obtained at 1.30 m above ground level was used. From the slice, sapwood and heartwood tablets were obtained and oriented in the three planes: radial, tangential, and transversal (De la Paz-Pérez and Dávalos-Sotelo 2008). The color was described using Munsell tables (1975). Texture, thread, grain, luster, and smell were classified according to Tortorelli (1956). The color, gloss, and smell were organoleptically tested.
For microscopic characterization, 4 slices of samples at 5 cm thickness obtained at different heights (0.30 m, 1.30 m, 3 m, and 6 m) were used. 2 by 2 cm cubes oriented in the transverse, tangential, and radial planes were cut (De la Paz-Pérez and Quintanar 1994), and the samples were labeled with the corresponding height data.
To make the histological cuts, the cubes were softened by boiling with distilled water for 8 h (De la Paz Pérez et al. 2015). The cuts were made with a Leica SMR2010 microtome (Leica, Buffalo Grove, IL, USA), and 15 μm thick lamellae were obtained in the following planes: transversal, tangential, and radial for sapwood and heartwood (De la Paz Pérez et al. 2006). Samples were stained by mixing distilled water, 96% alcohol, and safranin (García et al. 2003) dehydrated in a series of alcohols. The samples were finally rinsed in xylol for 2 min (Ruiz-Aquino et al. 2016). 50 permanent preparations were made by height for sapwood and heartwood (Navarro-Martínez et al. 2005).
For the preparation of the dissociation, small chips were cut from the material used for the histological cuts (Pineda et al. 2012). The small chips were placed in glass flasks. Glacial acetic acid and hydrogen peroxide at 30% were added (1 to 1 v per v) and were placed in the oven at 60 °C ± 5 °C for 24 h (Interián-Ku et al. 2011).
Measurements
The measurements were made on digital images from the Motic BA310LED optical microscope with an integrated camera and transferred to the Motic Images Plus ML Version 2.0 software (Motic, British Columbia, CA). The measurable elements (vessel elements, fibers, and rays) were classified based on the average according to Chattaway (1932) and the IAWA Committee (1937, 1939, 1989). 50 measurements were made per type of constituent element at each height and per type of wood. The length of the multi-serial rays was only measured 25 times (Valencia and Barajas 1995; Aguilar and Castro 2006; Chávez et al. 2010).
The vessel elements were classified in wide diameter (greater than 150 μm) and narrow diameter (less than or equal to 150 μm) (Chávez et al. 2010). The diameter and number of vessels per mm2 were measured on the cross-section of the histological sections and the length of the vessel elements in the dissociated material.
The length, overall diameter, lumen diameter, and cell wall thickness in the dissociated material were measured for the wood fibers. The number, cell number, and length of the uniseriate rays in the tangential section of the histological sections were recorded. The length of the multiseriate rays was measured with a Mitutoyo vernier (Mitutoyo, Aurora IL, USA) on the cross section of the wooden slats. The width and series number of the multiseriate rays were measured on the histological slices.
Pulp quality indexes for paper
Pulp quality indexes were calculated based on the following relationships given by Dadswell et al. (1959) and cited by Villaseñor-Araiza and Rutiaga-Quiñones (2000): stiffness coefficient (2 times the cell wall thickness per fiber diameter), flexibility coefficient (lumen diameter per fiber diameter), slenderness index (fiber length per fiber diameter), and Runkel index (2 times the cell wall thickness per lumen diameter). The classification of the pulp quality indexes for paper was based on the Runkel classification presented previously (Petroff and Nordman 1965; Porres and Valladares 1979) and cited by Villaseñor-Araiza and Rutiaga-Quiñones (2000). Group I (up to 0.25) was classified as excellent, Group II (from 0.25 to 0.50) was very good, Group III (from 0.50 to 1.00) was good, Group IV (from 1.00 to 2.00) was regular, and Group V (above 2.00) was unsatisfactory.
Physical properties
From each of the logs, 5 cm thick slices were cut at different heights (0.30 m, 1.30 m, 3 m, and 6 m). In each slice, sapwood and heartwood specimens were obtained according to the ASTM D 143-94 standard (2007). The physical properties determined were basic density, normal density (12% M. C.), green density, anhydrous density, volumetric, radial, tangential, and longitudinal shrinkage. The fiber saturation point (FSP) was calculated from Fuentes-Salinas (2000) equation as shown in Eq. 1,
FSP = VS × (0.9 × basic density)-1 (1)
where FSP represents the fiber saturation point, and VS represents volumetric shrinkage.
The anisotropy ratio (RA) was calculated according to Eq. 2,
RA = St × (Sr)-1 (2)
where RA represents the anisotropy ratio, St represents tangential shrinkage, and Sr represents radial shrinkage.
Chemical analysis
To determine the basic chemical composition of the wood of Q. macdougallii, wood samples were taken at different heights above ground level as mentioned earlier. From each slice, sapwood and heartwood were separated. This material was milled and sieved using the 40-mesh fraction. The chemical analysis included the determination of pH (Sandermann and Rothkamm 1959), the content of inorganic substances using the technique T 211 om-93 (TAPPI 2000), the solubility against organic solvents, the amount of lignin (Runkel and Wilke 1951), and the amount of holocellulose (Wise et al. 1946). For solvent solubility, a successive extraction in Soxhlet equipment was applied using cyclohexane, acetone, methanol, and finally hot water under reflux (Mejía-Díaz and Rutiaga-Quiñones 2008). In each case, the extraction lasted 6 h. Chemical analyses were performed in triplicate.
The inorganic elements in the ash were identified and quantified using an X-ray spectrometer connected to a Jeol JSM – 6400 scanning electron microscope (JEOL, Dearborn, MI, USA). The operating conditions were the same as reported by Téllez-Sánchez et al. (2010), 20 kV and 8.5 s.
Statistical analysis
A completely randomized experimental design was performed in which the four heights per type of wood (sapwood-heartwood) were compared. The parameters to be evaluated were the measurable anatomical elements (vessels, fibers, uniseriate, and multiseriate rays), pulp quality indexes, and physical properties (moisture content, basic density, anhydrous density, green density, normal density, volumetric shrinkage, fiber saturation point, linear shrinkage, and anisotropy ratio). For the anatomical elements, 50 repetitions per height were performed, and for the physical parameters, 18 repetitions per height. When significant differences in the parameters were found, a comparison of means was made using Tukey’s HSD test (α = 0.05). Statistical analysis was performed with the SAS® statistical package Version 9.0 (SAS Institute Inc., Cary, NC, USA).
RESULTS AND DISCUSSION
Macroscopic Anatomical
The wood of Q. macdougallii presented a very pale brown color (10YR8/2) in contrast to the heartwood, which is reddish yellow (5YR6/6). It has no characteristic smell, and the taste is bitter, a distinctive feature of the Quercus genus. This coincides with what has been reported for Q. magnoliifolia, Q. obtusata, and Q. crassifolia (Honorato 2002). The color, smell, and taste of the wood is given by the presence of extracts such as tannins and polyphenols that are deposited in the lumens and cell walls (De la Paz Perez 2000).
The brightness of the wood was medium (Fig. 1), a characteristic that occurs when the wood has annular porosity. The wood grain was pronounced, a feature that is determined by the vessels and the axial or longitudinal parenchyma. The wide multiseriate rays that make the grain more attractive also contribute to pronounced wood grain (Moglia et al. 2014).
The wood of Q. macdougallii presented a thick texture, a characteristic of the oaks Quercus castanea Née and Quercus acutifolia Née (De la Paz Pérez and Dávalos-Sotelo 2008). The thread of Q. macdougallii is straight and the woods with this characteristic present less shrinkage in contrast to woods that present inclined, spiral, or interlocked thread (León and Espinoza 2001). In addition, it facilitates the manufacture of turned and carved products.
Fig. 1. Macroscopic characteristics of Q. macdougallii wood: A) tangential section, B) cross section, C) radial section
Microscopic Anatomical Characteristics
Vessels
The wood of Q. macdougallii presented annular porosity, which is associated with medium or high densities, and are the most recommended in the manufacture of hand tools handles (hammers, axes, picks, shovels, among others). This is where the wood is subjected to impact stress. The force received perpendicular to the thread is dispersed mainly in the lumens of the larger vessels (Rodríguez et al. 2007).