The high decay resistance of western redeedar (Thuja plicata Donn) is due to the presence of toxic extractives, called tropolones, in the heartwood. Therefore, tropolone content may be used as an indicator of decay resistance. With increment core-sized samples of western redcedar heartwood, we used gas chromatography to measure tropolone content and soil block tests to assess decay resistance. Results showed that decay resistance was extremely variable at low tropolone levels, but was uniformly high at tropolone levels of 0.25% or greater. Analyzing tropolone content of western redeedar increment cores is a useful way to assess decay resistance of standing trees

DeBell, Jeffrey D.

Gartner, Barbara L.

Morrell, Jeffrey J.

English

Wood and Fiber Science (E-Journal)

TROPOLONE CONTENT OF INCREMENT CORES AS AN INDICATOR OF DECAY RESISTANCE IN WESTERN REDCEDAR Jeffrey D. DeBelll Former Graduate Research Assistant Jeffrey J. Morrell Associate Professor and Barbara L. Gartner Assistant Professor Department of Forest Products Forest Research Laboratory Oregon State University Corvallis, OR 9731 1-7402 (Received January 1997) The high decay resistance of western redcedar (Tl>ujo plicntrr Donn) is due to the presence of toxic extracti~~cs, called tropolones, in the he;trtwood. Therefore, tropolone content may he used as an indicator of decay resistance. With increment core-sized samples of western redcedar heartwood, we used gas chromatography to measure tropolone content and soil hlock tests to assess decay resistance. Results showed that decay resistance was extremely variahle at low tropolone levels, but was uniformly high at tropolone levels of 0.25% or greater. Analyzing tropolone content of western redcedar incre- ment cores is a useful way to assess decay resistance of standing trees. Keywords: Tlrrrja plicotn, tropolones, thujaplicins. decay resistance Westem redcedar (Thuja plicata Donn) is a valuable commercial species in the northwest- em United States and Canada. One of its most important characteristics is high decay resis- tance, which is due to the presence of toxic extractives in the heartwood. While a number of heartwood extractives have been shown to be toxic to fungi, the tropolones are the most important; they are comparable to pentachlo- rophenol in toxicity (Barton and MacDonald 1971; Rennerfelt 1948; Rudman 1962, 1963). Five tropolones have been identified in west- ' Present address: Natural Resource Scientist. Washing- ton Dept. of Natural Resources, PO. Box 47018. Olympia. WA 98504-7018. em redcedar. Of these, P-thujaplicin, y-thuja- plicin, and P-thujaplicinol are the most impor- tant in terms of quantity, together making up 98% of the total tropolone content (Barton and MacDonald 197 1 ; Frazier 1987). Since tropolones are primarily responsible for the decay resistance of westem redcedar, it should be possible to use tropolone content of the wood as an indicator of decay resistance. Tropolone content can he assessed in days; the standard method of assessing decay resistance is the soil block test, which takes 12-16 weeks. Nault (1988) noted that measurement of tropolones using gas chromatography can he accomplished with very small samples, making it possible to use increment cores to assess tropolone content of standing trees. Wrld i z f a l  1;;br.r .Srlu,icc.. 29141. 1,197, pp. 3Cr1-36" "1 1'107 hy Ihc Soclcly of Wood Sricnrc :>nd Tcchnnlng) I>eR,dl er 01.-TROPOLONE CONTENT AND DECAY RESISTANCE IN WESTERN REDCEDAR 365 This would be particularly useful for studying tropolone content in situations where destruc- tive sampling is undesirable. Techniques have been developed previously for measuring thujaplicin content using gas chromatography (Johnson and Cserjesi 1975, 1980; Nault 1987, 1988). The first step is ex- traction in a soxhlet apparatus; thus, the num- ber of samples that can be processed at one time is limited by the number of soxhlet setups available. For some studies, it would be desir- able to use an extraction method that allows more efficient processing of large numbers of samples. We modified the technique of Johnson and Cserjesi (1980) to allow efficient handling of large numbers of increment cores or similar sized samples. We then used the technique on small samples collected from various positions within the heartwood of western redcedar trees. This paper is limited to an examination of the technique, including its repeatability and the relationship between tropolone content and decay resistance; variation of tropolone content and decay resistance as a function of position in the stem will be discussed in an- other paper. METHODS Collection of' wood samples Material for this study came from western redcedar trees growing near Clatskanie, Ore- gon, on the Oregon State University College of Forestry's Blodgett Tract. Eleven trees were felled (Table I), and disks were cut every 2 m from breast height (1.37 m) to the top of the tree. The disks were taken to the lab, where they were air-dried. A drill equipped with a 9.5-mm plug cutter was used to remove two plugs, parallel to the stem axis and oriented side by side tangentially, from the outermost heartwood of each disk. A second pair of plugs was removed approximately 1.5 cm from the pith. One of the plugs from each pair was used for tropolone analysis, while the oth- er was used in the decay tests. We selected the plug size because it is close to the diameter of TABLE 1. Selecred chomcren'.srics of .srrmple frees. li,,;,1 ('nwn Trcree hsieht im l  RH ape Peiccnt DRH (cml the 8-mm increment cores we often use in wood quality studies. Tropolone ana1y.si.s We modified the extraction technique of Johnson and Cserjesi (1980) by replacing soxhlet extraction with cold extraction in cen- trifuge tubes. The benefit of this modification was the ability to process larger numbers of samples quickly. The disadvantage was that complete extraction was not possible. Thus the method is suitable for studying relative differ- ences in tropolone content between wood sam- ples rather than absolute tropolone content of a sample. Rased on a few comparisons we made, cold extraction is capable of extracting 90% or more of the tropolones extracted by the soxhlet method. Each redcedar plug was cut into pieces and ground in a small Wiley mill to pass through a 30-mesh screen. Approximately 0.5 g (tO.O1 g) of wood meal from each sample was weighed and placed in a 50-ml plastic centrifuge tube, along with 9 ml of acetone and 1 ml of an internal standard solution (3.4,s-trimethoxyphenol in acetone, with 0.35 mglml). The tube was capped and allowed to sit overnight (16 h) at room temperature (23- 25°C). The sample was then centrifuged for 5 min, and the extract was transferred by Pasteur pipet to a clean 50-ml plastic centrifuge tube. The samples were evaporated to I ml by WOOD AND F'IBBR SCIENCE, OCTOBER 1997. V. 29(4) s.c c =2 z r 2% 0-33 I . Retention Time (rnin) Rc. 1. Typical chromatogram showing retention times for 3.4.5-trimethoxyphenol, P-thujaplicin, y-thujaplicin, and @-thujaplicinol. blowing air through a small hose into the tube. The sample was then transferred to a small glass vial, and evaporated to dryness using air as described above. When the sample was dry, 0.2 ml of B.S.A. (N,O-bis (trimethylsilyl) acetamide) was added, and the sample was placed in a warming tray at 70°C for 10 min. A needle and syringe were then used to trans- fer the solution to an autosampler vial, which was capped and placed in the autosampler tray to await injection into the gas chromatograph. One-microliter injections were made. A Hewlett Packard HP-5890 gas chromato- graph equipped with a flame ionization detec- tor and an autosampler was used for analyses. The column was a Supelco SPB-5 (30 m X 0.75 mm). Hydrogen was the carrier gas, with a flow rate of 15 ml/min. The initial oven tem- perature of 125°C was held for 4 min, then raised at S°C/min to 200°C. Injector and de- tector temperatures were 250°C. Retention times for the internal standard and tropolones were as follows (Fig. 1): 3,4,5-trimethoxy- phenol: 9.9 min; P-thujaplicin: 10.4 min; y-thujaplicin: 11.0 min; P-thujaplicinol: 14.6 min. Tropolone content was determined by com- parison of tropolone peak areas with that of the internal standard. Pure samples of y-thu- japlicin and P-thujaplicinol were provided by Forintek Canada Corporation. P-thujaplicin was purchased under the name Hinokitiol from a commercial supplier (TCI America). Tropolone content was expressed as a per- centage of air-dried wood weight. Small-scale analyses In addition to analyzing tropolone content in the samples described above, we ran two small scale tests to check the precision of the method, and to assess the variation in tropo- lone level around the outer heartwood of a western redcedar tree. The precision of the method was checked by separately analyzing 5 subsamples of a single bulk sample of ground cedar heartwood. The variation in tro- polone content around an individual stem was DeBell er 01.-TROPOLONE CONTENT AND DECAY RESISTANCE IN WESTERN REDCEDAR 367 Ro. 2. Positions of samples removed from a western redcedar disk to assess variation in tropolone content around the circumference of the stem. assessed by analyzing 16 plugs from a single disk, as shown in Fig. 2. Soil block tests Soil block tests were performed using pro- cedures described by Scheffer et a]. (1987). Briefly, 113-ml glass bottles were half-filled with moist forest loam, and a single 15 X 15 X 3-mm-thick western hemlock (Tsuga het- erophylla (Raf.) Sarg.) feeder strip was placed on the soil surface. Water was added to raise the moisture content to 100% (weight basis); then the jars were loosely capped prior to au- toclaving for 45 min at 121°C. After cooling, the feeder strips were inoculated with 3-mm- diameter disks of agar cut from the actively growing edge of cultures of Postia placenta (Fr.) M. Larson & Lombard, a fungus which causes brown rot of many coniferous species. The bottles were incubated at 28°C until the feeder strips were thoroughly colonized by the test fungus. The cedar heartwood plugs were oven-dried (54'C), weighed, and sealed in plastic bags and subjected to 2.5 Mrads of ion- izing radiation from a cobalt 60 source. The plugs were placed on the feeder strips (1 plug1 bottle) and the jars were then incubated at 28'C for 16 weeks. The plugs were removed, scraped clean of adhering mycelium prior to oven-drying (54°C). and weighed. Loss in oven-dried weight was used as the measure of decay resistance (samples with the least FIG. 3. Variation in heartwood tropolone content around the circumference of a western redcedar stem. weight loss were considered the most decay- resistant). RESULTS AND DISCUSSION Small-scale analyses The coefficient of variation for tropolone content of the five subsamples from a single batch of cedar meal was 4.5%. This low level of variation indicates that the modified method gives consistent results; we consider this level of precision to be acceptable for wood quality studies. Tropolone content around the outer heart- wood was fairly uniform around most of the disk, averaging between 0.2 and 0.3% (Fig. 3). But samples from the 180 degree position con- tained nearly double the tropolone content of samples from the rest of the disk. There was no obvious reason for the higher level at this position. From these data, it appears that a sin- gle increment core should be a useful indicator of tropolone content at a given location in a tree. With a single core, the tropolone content of some trees could be significantly over- or underestimated if an increment core includes an atypical zone like the one we encountered at the 180 degree position (Fig. 3). If only a few trees are sampled, average tropolone con- tent at the sampling height could also be over- or underestimated. In this case, one might want to get several samples per tree to im- prove the reliability of the estimate for each tree. However, if the sample size (number of 368 WOOD AND FIBER SCIENC :E, OCTOBER 1997. V. 29(4) FIG. 4. Relationship between tropolone content and weight loss in soil block tests for paired samples of west- ern redcedar heartwood. trees) is large enough, the effect of hitting an atypical zone in a few trees should be unim- portant to the overall results, and the extra work of collecting multiple cores from each tree may not be justified. The consistency in tropolone content at po- sitions where clusters of three samples were taken increased our confidence in the precision of the method (Fig. 3). The data also suggest- ed that if multiple increment cores are taken from a single tree, the cores should be sepa- rated by at least 90 degrees, since taking two cores near the same point may do little to im- prove the estimate of the average troplone content at that height in the tree. Relationship of tropolone measurements to soil block tests Tropolone content of the wood samples ranged from 0 to 1.2% (weight basis), while weight loss ranged from 0 to 70% (Fig. 4). Weight loss was highly variable for samples with tropolone content <0.10%, but averaged 21% loss. Weight loss was less variable for samples with tropolone contents between 0.10% and 0.24%, averaging 9% loss. Sam- ples with tropolone content 20.25% had con- sistently low weight loss; average weight loss was 4%. Only 3 out of the 59 samples with high tropolone content had more than 10% weight loss. We are unsure of the reasons for the high variability in weight loss in samples with low tropolone levels. One possibility is that other substances in the heartwood prevented signif- icant decay in some samples. However, there were no obvious patterns in the chromato- grams to suggest any major differences in oth- er extractives between low tropolone samples. Differences in tropolone distribution could in- fluence the results, since the extract and decay samples were separate but adjacent plugs; however, the results from repeated sampling of a single disk (Fig. 3) suggest that these dif- ferences should be minimal. The variability of the soil block test may be a factor, since in- dividual decay tests can sometimes vary wide- ly. These results indicate that tropolone analy- sis of increment cores is a useful way to assess decay resistance at a given position in standing trees. The modified analysis method, using cold extraction, gave consistent results and could be used with large numbers of samples efficiently. This technique should be particu- larly useful for wood quality studies, where many trees must be sampled. ACKNOWLEDOMENTS We are indebted to Bob Daniels of Forintek Canada Corporation for supplying tropolone samples and discussing extraction techniques when we began this project. We also thank Associate Professors Chris Biermann, Joe Karchesy, and Murray Laver of Oregon State University's Department of Forest Products for providing us with laboratory equipment and valuable technical assistance. This re- search was funded by a USDA Special Grant to Oregon State University for Wood Utiliza- tion Research. REFERENCES BARTON, G. M., AND R.  F MACDONALD. 1971. The chern- ismy and utilization of western red cedar. Canadian For. Serv. Publ. No. 1023. 31 pp. F R A ~ E R .  C. E. 1987. The essential oil of western red cedar, (Thuja plicata). M.S. thesis. University of Wash- ington, Seattle, WA. 112 pp. JOHNSON, E. L., AND A. J .  CSERJESI. 1975. Gas-liquid DeBell er ol-TROPOLONE CONTENT AND DECAY RESISTANCE IN WSTERN REDCEDAR 369 chromatography of some hopolone-TMS ethers. J .  Chromatog. 107(21:388. -, AND - 1980. Weathering effect on thuja- plicin concentration in western redcedar shakes. Forest Prod. 1. 30(6):52-53. NAILT, 1. 1987. A capillary gas chromatographic method for thujaplicins in western redcedar extractives. Wood Sci. Technol. 21(4):311-316. -. 1988. Radial distribution of thujaplicins in old growth and second growth western red cedar (Thuja plicarn Donn). Wood Sci. Technol. 22(1):73-80. RT;NNERFW.T, E. 1948. Investigations of thujaplicin, a fun- gicidal substance in the heartwood of Thttja plicntn D. Don. Physiologia Plantarum 1(1):245-254. RIJDMAN, F! 1962. The causes of natural durability in tim- ber. IX. The antifungal activity of heartwood extractives in a wood substrate. Holzforschung 16(3):74-77. -. 1963. The causes of natural durabiltity in timber. Part XI. Some tests on the fungi toxicity of wood ex- tractives and related compounds. Holzforschung 17(2): 54-57. SCHEFFER. T. C., 1. J .  MORREII.. AND M. A. NFWRII.L. 1987. Shellrot control in western redcedar: potential re- placements for pentachlorophenol spray. Forest Prod. I. 37(7/8):51-54. 

Tropolone Content of Increment Cores as an Indicator of Decay Resistance in Western Redcedar

https://wfs.swst.org/index.php/wfs/article/download/1315/1315

Tropolone Content of Increment Cores as an Indicator of Decay Resistance in Western Redcedar

Abstract

Similar works

Full text

Available Versions

Wood and Fiber Science (E-Journal)