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Purusatama, B. D., Kim, S. W., and Kim, N. H. (2024). “A comparative study on quantitative anatomical characteristics of compression, lateral, and opposite woods in Agathis loranthifolia and Pinus merkusii,” BioResources 19(1), 925-943.

Abstract

Quantitative anatomical characteristics and their radial variation in compression (COW), lateral (LAW), and opposite (OPW) woods of Agathis loranthifolia and Pinus merkusii stem woods growing in Indonesia were observed and compared to understand wood quality. The length, diameter, wall thickness, and lumen diameter of tracheids and ray height and numbers were observed using optical microscopy. In both species, COW had the shortest tracheid length, smallest tracheid and lumen diameter, thickest cell wall, and highest ray numbers among the parts, while LAW and OPW showed comparable or variable values in quantitative characteristics. In A. loranthifolia, COW had the highest ray height, whereas, in P. merkusii, it had the lowest uniseriate and fusiform ray heights. No significant difference was observed in ray numbers and heights between LAW and OPW. In both species, the tracheid length and lumen-to-diameter ratio in COW, LAW, and OPW tended to increase from near the pith to near the bark while the wall-to-diameter ratio decreased. The ray heights of all parts increased with increasing distance from the pith, whereas the ray number decreased.

 


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A Comparative Study on Quantitative Anatomical Characteristics of Compression, Lateral, and Opposite Woods in Agathis loranthifolia and Pinus merkusii

Byantara Darsan Purusatama,a Suk Woo Kim,b and Nam Hun Kim c,*

Quantitative anatomical characteristics and their radial variation in compression (COW), lateral (LAW), and opposite (OPW) woods of Agathis loranthifolia and Pinus merkusii stem woods growing in Indonesia were observed and compared to understand wood quality. The length, diameter, wall thickness, and lumen diameter of tracheids and ray height and numbers were observed using optical microscopy. In both species, COW had the shortest tracheid length, smallest tracheid and lumen diameter, thickest cell wall, and highest ray numbers among the parts, while LAW and OPW showed comparable or variable values in quantitative characteristics. In A. loranthifolia, COW had the highest ray height, whereas, in P. merkusii, it had the lowest uniseriate and fusiform ray heights. No significant difference was observed in ray numbers and heights between LAW and OPW. In both species, the tracheid length and lumen-to-diameter ratio in COW, LAW, and OPW tended to increase from near the pith to near the bark while the wall-to-diameter ratio decreased. The ray heights of all parts increased with increasing distance from the pith, whereas the ray number decreased.

DOI: 10.15376/biores.19.1.925-943

Keywords: Agathis loranthifolia; Compression wood; Lateral wood; Opposite wood; Pinus merkusii; Quantitative anatomical characteristics

Contact information: a: Institute of Forest Science, Kangwon National University. Chuncheon 24341, Republic of Korea; b: Division of Forest Science, Kangwon National University, Chuncheon 24341, Republic of Korea; c: Department of Forest Biomaterials Engineering, College of Forest and Environmental Sciences, Kangwon National University, Chuncheon 24341, Republic of Korea;

* Corresponding author: kimnh@kangwon.ac.kr

INTRODUCTION

Compression wood (COW) is classified as an abnormal wood tissue in conifers resulting from a response to mechanical stress experienced by a tree. In the stem wood, COW tends to push back, leaning the stem back to the vertical position, whereas in the branch wood, COW maintains the position of the branch against gravity. COW occurs on the lower side of a leaning stem and branches of conifers. Lateral woods (LAW) and opposite woods (OPW) also occur. The transverse surface of COW in the stem or branch commonly shows a darker brown or reddish color compared to the lateral and opposite sides (Timell 1973; Park 1979 and 1980; Purusatama and Kim 2018). In qualitative characteristics, the tracheid of COW typically shows a circular shape with a highly lignified S2 layer and helical cavities in the cell wall, frequently surrounded by intercellular spaces (Timell 1986; Purusatama et al. 2018; 2021). In quantitative analysis, COW comprises a shorter tracheid length, smaller radial diameter, lower relative crystallinity, and smaller crystallite width compared to LAW and OPW. In addition, no significant differences exist in pit number and diameter in the cross-field of Pinus densiflora and Ginkgo biloba between COW, LAW, and OPW (Purusatama et al. 2020; Purusatama and Kim 2020).  LAW and OPW of G. biloba tended to show comparable tracheid length, ray height, and ray number (Purusatama et al. 2018). Besides, in temperate conifers, LAW and OPW showed a difference in tracheid diameter and cell wall thickness (Kienholz 1930; Park et al. 1979; Eom and Butterfield 1997; Eom and Butterfield 2001; Yong et al. 2022)

A. loranthifolia and P. merkusii, which are commonly distributed in mountain areas of Indonesia, are fast-growing wood species widely planted in Indonesian plantation forests. Both wood species are generally utilized for paneling, molding, packaging, furniture, musical instruments, and the raw materials for pulp and paper (Martawijaya et al. 2005; Darmawan et al. 2018; Trisatya et al. 2021). The wood of both species shows comparable mechanical properties with commercial temperate softwoods such as Korean red pine and Sitka spruce (Nugroho and Surjokusumo 2002; Darmawan et al. 2018). However, compression wood frequently occurs in both species, which is a challenge for the Indonesian wood industry.

Understanding the characteristics of a woody stem is essential in evaluating wood quality and technical application. Specifically, the qualitative and quantitative anatomical characteristics of wood are valuable information for wood quality evaluation. To date, studies on the qualitative and quantitative anatomical characteristics of reaction wood in tropical softwood are limited.

Qualitative studies of reaction wood in tropical softwoods revealed that the helical cavity was absent in COW from Agathis spp., Araucaria spp., and Agathis robusta (Westing 1965; Timell 1986). A mild COW rich in lignin in the S2 layer, helical cavity, and round shape of tracheid was found in Araucaria brasiliana (Yoshizawa and Idei 1986). Pandit and Rahayu (2007) reported that the COW of A. loranthifolia showed a circular shape tracheid in the transverse surface and helical cavities in the radial section, and S3 was absent in the COW. Kim et al. (2015) revealed that mild COW of Agathis borneensis consistently showed intercellular spaces and high lignification in the outer part of the S2 layer, while the rounded-shaped tracheid and helical cavities were absent. Purusatama et al. (2021) indicated that COW of P. merkusii and A. loranthifolia showed distinctive qualitative anatomical characteristics compared to LOW and OPW as helical cavities, slit-like bordered pit, and irregular arrangement of tracheid. They also found that helical ribs occurred in the COW of P. merkusii but were absent in the COW of A. loranthifolia.

For quantitative analysis of reaction wood in tropical softwoods, Purusatama et al. (2022) examined the COW, LAW, and OPW in P. merkusii and A. loranthifolia and revealed that COW and OPW in P. merkusii showed comparable tangential tracheid diameters. In contrast, COW had a significantly smaller tangential lumen diameter and tangential wall thickness than that for LAW and OPW. In A. loranthifolia, COW showed the smallest tangential tracheid and lumen diameters and the thickest tangential wall thickness among the parts, whereas LAW and OPW showed comparable tracheid characteristics. Safitri et al. (2023) reported that COW and OPW in P. merkusii seedlings showed comparable tracheid length, diameter, wall thickness, and ray frequency, whereas COW showed a significantly higher ray height and smaller tracheid proportion compared to OPW.

Studies on the radial variation of quantitative anatomical characteristics of COW, LAW, and OPW are few. Kienholz (1930) revealed that the tracheid length and diameter in COW, OPW, and side wood of Tsuga mertensiana increased with increasing growth ring number. Park et al. (1979; 1980) reported that the tracheid diameter and the cell wall thickness in COW, OPW, and side wood of Pinus densiflora branch wood increased from pith to bark, and the microfibril angles of all parts decreased. Purusatama and Kim (2018) revealed that the tracheid length and ray height of COW, LAW, and OPW in Gingko biloba stem wood increased from the 5th to 20th growth ring, whereas the ray number decreased. Purusatama and Kim (2020) showed that the radial tracheid diameter of COW in Gingko biloba increased with the increasing distance from the pith, whereas that in Pinus densiflora decreased. The radial tracheid diameter of LAW and OPW in Gingko biloba and Pinus densiflora was constant from the pith toward the bark.

To date, studies on the qualitative and quantitative anatomical characteristics of COW, LAW, and OPW in the stem of tropical softwood, including the radial variation, are lacking. A previous study revealed the difference in qualitative anatomical characteristics between COW, LAW, and OPW and between A. loranthifolia and P. merkusii (Purusatama et al. 2021). In this study, the quantitative anatomical characteristics of COW, LAW, and OPW in A. loranthifolia and P. merkusii were observed and compared in the radial direction to provide valuable information for effectively utilizing both species.

EXPERIMENTAL

Materials

The information on the sample trees used in the present study is similar to that of previous studies (Purusatama et al. 2020; 2021; 2022). A 65-year-old Agathis loranthifolia tree and a 49-year-old Pinus merkusii tree, each having a tilt of the stem axis close to 45° were obtained from Gunung Walat University Forest, Sukabumi, West Java, Indonesia (6.882937° N, 106.818511° E) (Fig. 1). The wood discs with a diameter of approximately 400 mm were taken from a height of 4 m above the ground. The wood disc was divided into three parts: COW, LOW, and OPW (Fig. 1).

Fig. 1. Fresh-cut wood discs of Agathis loranthifolia (left) and Pinus merkusii (right). NP, middle zone, and NB are represented with 1, 2, and 3, respectively. Scale bars = 100 mm

The quantitative anatomical characteristics of each part were observed in three zones according to the distance from the pith, such as near the pith (NP), middle zone, and near the bark (NB). The NP, middle zone, and NB in COW were 50, 200, and 350 mm from the pith (Fig. 1).

Microscopy

Measurement of tracheid length

For the tracheid length measurement, matchstick-sized specimens of approximately 1 mm wide and 20 mm to 30 mm in length were prepared from each zone of COW, LAW, and OPW. The samples from each part were soaked in Schultze reagent (100 mL of 35% nitric acid [HNO3] and 0.6 g of 99.5% potassium chlorate [KClO3]) for three days and heated at 60 to 70 °C for 1 h (Park et al. 1993; Savero et al. 2022). The samples were stirred several times until they were unraveled during the heating process. Tracheid length was measured randomly with 50 tracheids using a measuring microscope (MM-40; Nikon, Tokyo, Japan) connected to an image analysis software (IMT i-solution lite, version 9.1; Burnaby, British Columbia, Canada).

Measurement of tracheid and ray properties

Wood discs were converted to small blocks (10 mm3) and soaked in a mixture of glycerin and water (50:50). Then, the samples were heated with a heating plate for 30 to 45 min. Cross and tangential sections with a 15 to 20 µm thickness were prepared using a sliding microtome (Nippon Optical Works Co, Ltd., Tokyo, Japan). All slices were stained with 1% safranin solution and dehydrated by a graded series of alcohol (50%, 70%, 90%, 95%, and 99%) and xylene. Canada balsam was used as a mounting medium for permanent slides.

The tracheid diameter, lumen diameter, and tracheid wall thickness on the cross-section were measured from 50 earlywood tracheids according to Cuny et al. (2014), as shown in Fig. 2. The double wall thickness was determined by calculating the difference between the diameter of the tracheid and that of the lumen. The ratios of the lumen-to-diameter and wall-to-diameter in the radial and tangential directions were measured from 50 earlywood tracheids.

Fig. 2. Illustration of tracheid dimension measurement on the cross-section. TLD and TTD represent tangential lumen and tracheid diameters, while RLD and RTD are radial lumen and tracheid diameters, respectively

Ray number was measured in 20 areas of 1 × 1 mm2 microscopic screen in tangential sections. The ray height of uniseriate and fusiform rays was randomly measured from 50 rays in each zone of COW, LAW, and OPW. The tracheid and ray properties were observed with an optical microscope (Eclipse E600; Nikon, Tokyo, Japan) with image analysis software (IMT i-solution lite, version 9.1; Burnaby, British Columbia, Canada).

Statistical Analysis

One-way analysis of variance and post-hoc Duncan’s multiple range tests were used to analyze the significant differences in the quantitative anatomical characteristics between COW, LAW, and OPW and between NP, middle zone, and NB using SPSS software (SPSS ver. 26, IBM Corp., New York, USA).

RESULTS AND DISCUSSION

Tracheid Lengths

The tracheid lengths in COW, LAW, and OPW of A. loranthifolia and P. merkusii are shown in Table 1. Near the pith of A. loranthifolia, COW had a comparable tracheid length to LAW, and OPW had the longest tracheid length. Compression wood had the shortest tracheid length in the middle zone and near the bark, whereas LAW and OPW showed no significant differences. Regarding the average tracheid length, the COW of both species had the shortest tracheid length, whereas LAW and OPW were similar in length. In P. merkusii, no significant difference in the tracheid length was observed in COW, LAW, and OPW near the pith. Compression wood had the shortest tracheid length in the middle zone and near the bark. Lateral wood had the longest tracheid length in the middle zone, whereas OPW had the longest tracheid length near the bark. The tracheid lengths of COW, LAW, and OPW from both species increased from near the pith to near the bark.

In the present study, the tracheid length of all parts near the pith of both species showed a comparable length, whereas significant differences were observed in the middle zone and near the bark. In addition, the tracheid length of COW, LAW, and OPW in both species increased from pith to bark. Kienholz (1930) revealed that the compression and opposite side of Tsuga mertensiana had a comparable tracheid length at the 11th to 21st growth rings (near the pith). In contrast, the tracheid length of the compression side was distinctively shorter than the opposite side at the 31st to 81st growth rings. Wardrop and Dadswell (1950) reported that the tracheid length of the compression side near the pith (3rd to 9th growth rings) of Pinus radiata stem wood was comparable with the opposite side. The compression side had a shorter tracheid than the opposite side from the 10th to 20th growth rings. Purusatama and Kim (2018) reported that in the stem wood of Ginkgo biloba, COW and OPW had similar tracheid lengths at the 5th and 10th growth rings, and LAW had the longest. Furthermore, COW had the shortest tracheid length at the 15th to 20th growth rings, whereas LAW and OPW had similar tracheid lengths. Regarding the radial variation, the tracheid lengths of reaction wood in Tsuga mertensianaPinus radiata, and Gingko biloba increased with increasing growth ring numbers (Kienholz 1930; Wardrop and Dadswell 1950; Purusatama and Kim 2018).

The average tracheid length of COW, LAW, and OPW in A. loranthifolia and P. merkusii was categorized as medium length according to the IAWA list for softwood identification (IAWA Committee 2004). The average tracheid length of reaction wood in both species was noticeably longer than those of temperate reaction wood, such as Tsuga mertensiana (Kienholz 1930), Pinus radiata (Wardrop and Dadswell 1950), and Gingko biloba (Purusatama and Kim 2018), which is categorized as short according to the IAWA list for softwood identification (IAWA Committee 2004).

Table 1. Tracheid Length: COW, LAW, and OPW; A. loranthifolia and P. merkusii

Tracheid Diameter, Lumen Diameter, and Wall Thickness

The cross-sections of COW, LAW, and OPW in A. loranthifolia and P. Merkusii are shown in Figs. 3 and 4, respectively.

Fig. 3. The cross-section of COW, LAW, and OPW near the pith (NP), middle zone, and near the bark (NB) of A. loranthifolia. Intercellular spaces in COW (white arrows). Scale bars: 50 µm

Fig. 4. The cross-section of COW, LAW, and OPW near the pith (NP), middle zone, and near the bark (NB) of A. loranthifolia. Intercellular spaces in COW (white arrows); Round lumen near the pith of COW (black arrows). Scale bars: 50 µm

In A. loranthifolia, the COW in each zone showed typical anatomical features with circular tracheid shapes and several intercellular spaces. In contrast, LAW and OPW showed oval lumens with angular outlines and no intercellular spaces. Near the pith of P. merkusii, the tracheid of COW showed a round lumen with an angular outline with no intercellular space. In the middle zone and near the bark, COW displayed circular tracheid shapes and numbers of intercellular spaces. Lateral wood and OPW near the pith and in the middle zone exhibited angular lumens and tracheid outlines, whereas near the bark of both parts showed oval tracheid lumens with angular outlines.

Table 2 shows the tracheid diameters in the radial and tangential directions of COW, LAW, and OPW in A. loranthifolia and P. Merkusii. In A. loranthifolia, COW near the pith had the greatest radial tracheid diameter, whereas LAW and OPW showed comparable values. The tangential tracheid diameters of COW and LAW were comparable, and OPW had a greater tangential tracheid diameter than that of COW and LAW. In the middle zone and near the bark, COW had the smallest radial and tangential tracheid diameter among all parts. Lateral wood in the middle zone had a significantly smaller radial tracheid diameter than that of OPW, whereas the tangential tracheid diameter of LAW was significantly greater than that of OPW. Furthermore, OPW near the bark had a significantly greater radial tracheid diameter than that of LAW, whereas LAW and OPW had comparable tangential tracheid diameters. COW had the smallest average value of radial and tangential tracheid diameter. Lateral wood had a significantly smaller radial tracheid diameter than that of OPW, whereas the tangential tracheid diameter was comparable between LAW and OPW. The tracheid diameter of COW decreased from near the pith to near the bark, whereas that of LAW and OPW increased.

Compression wood in each zone of P. merkusii had the smallest radial tracheid diameter. Near the pith and bark of P. merkusii, LAW and OPW had comparable radial tracheid diameters. In the middle zone, LAW had a significantly greater radial tracheid diameter than that of OPW. Near the pith of P. merkusii, the tangential tracheid diameter of COW was greater than that of OPW, whereas LAW had the greatest tangential tracheid diameter. In the middle zone, the tangential tracheid diameter of COW was the smallest, and that of LAW was the greatest. Near the bark, COW, LAW, and OPW had comparable tangential tracheid diameters. Compression wood had the smallest average value of radial and tangential tracheid diameters, whereas LAW had a significantly greater tracheid diameter than that of OPW. Significant differences were observed in the average tracheid diameter in radial and tangential directions between the parts. The tracheid diameter of COW, LAW, and OPW in P. merkusii increased from near the pith to near the bark.

Table 2. Tracheid Diameter in COW, LAW, and OPW of A. loranthifolia and P. merkusii

Table 3 shows the lumen diameters in the radial and tangential directions of COW, LAW, and OPW in both species. In A. loranthifolia, COW, LAW, and OPW near the pith showed no significant difference in the radial lumen diameter. Compression wood had the smallest lumen diameter in the middle zone and near the bark. The radial lumen diameter of LAW was significantly smaller than that of OPW in the middle zone and near the bark. The tangential lumen diameter of LAW and OPW was comparable in the middle zone, whereas LAW near the bark showed a significantly smaller tangential lumen diameter compared to OPW. The lumen diameter of COW decreased from near the pith to near the bark, whereas that of LAW and OPW increased.

The lumen diameter of COW in each zone of P. merkusii had the smallest value among all parts. Near the pith of P. merkusii, LAW had a significantly smaller radial tracheid lumen diameter than that of COW, whereas LAW and OPW had comparable tangential tracheid lumen diameters. In the middle zone, the tracheid lumen diameter of LAW was significantly greater than that of COW and OPW, whereas no significant difference was observed in the tracheid lumen diameter of LAW and OPW near the bark. The lumen diameter of COW, LAW, and OPW in P. merkusii increased from near the pith to near the bark.

Table 3. Lumen Diameter in COW, LAW, and OPW of A. loranthifolia and P. merkusii