IAWA Bulletin n.s., Vol. 10 (2),1989: 201-207

WOOD ANATOMICAL VARIATION OF ACACIA MELANOXYLON IN RELATION TO LATITUDE

by

A. P. Wilkins and Sabine Papassotiriou Forestry Commission of New South Wales, P. O. Box 100, Beecroft, Sydney, 2119, Australia

Summary The wood anatomy of Acacia melanoxy­ one of the most useful furniture and cabinet Ion samples from various locations in eastern timbers of Australia. Typically, the wood Australia was examined and a number of anatomy shows distinct growth rings with characteristics were found to be significant­ dense latewood bands, vessels which are ly related to latitude. Vessel member length, solitary or in short radial multiples, vessel proportion of fibres and proportion of multi­ diameter between 100-300 j.1m, some para­ seriate rays were positively related to latitude. tracheal parenchyma, homogeneous 1-3-seri­ Vessel frequency, vessel diameter and the ate rays and up to 40 cells high (Dadswell & abundance of crystals were negatively related Eckersley 1935). to latitude as were the proportion of: uniseri­ The species is distributed in eastern Aus­ ate rays, vessels and axial parenchyma. Total tralia between 16 and 43° latitude (Fig. I), at proportion of ray tissue and basic density altitudes from sea level to 1500 m (usually was not found to be associated with latitude. < 1300 m) and generally within 200 km from Anatomical features associated with lower the coast (Farrell & Ashton 1978; Boland et transpirational demand appeared to be corre­ al. 1965). Climatic variation over this geo­ lated with the cooler, more xeric environ­ graphical range is large. Mean annual rainfall mental conditions accompanying increasing is generally from 750-1500 mm; however, latitude. rainfall has a winter maximum in the southern Key words: Acacia melanoxylon RBr., wood cool temperate zone, an even distribution in anatomy,latitudinal variation. the central warm temperate zone and a sum­ mer maximum in the northern subtropical and futroduction tropical zones of Queensland. The more se­ The genus Acacia is generally considered vere winter frosts and drier summers asso­ to consist of approximately 1200 species ciated with increasing latitude produce more (Pedley 1986). The wood anatomy of the xeric environmental conditions, particularly genus has been described in a general way in Tasmania. (Metcalfe & Chalk 1950); however, little has An examination of the vessel characteris­ been reported for individual species (Dads­ tics of 15 Australian species of Acacia sug­ well & Eckersley 1935; Robbertse et al. gested that anatomical variation in this genus 1980; Ford 1984; Fahn et al. 1986). may be related to environment (Ford 1984). Acacia melanoxylon R. Br. (blackwood) This study examined wood anatomical varia­ is one of the largest and most commercially tion of A. melanoxylon in relation to latitude. important acacias. Usually a tree of 10-20 m height, it varies from a multistemmed shrub Methods in open situations to a tree of up to 47 m in Wood samples were obtained from herba­ northern Tasmania where it attains its best ria and forestry organisations in eastern Aus­ development (Farrell & Ashton 1978; Boland tralia. Samples were grouped according to et al. 1985). The wood is golden brown in their state of origin: Queensland (9 samples), colour, sometimes with reddish streaks. It is New South Wales (6 samples), Victoria (4

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Vessel frequency was determined by count­ ing individual vessels (not multiples), using the method of Lanyon (1981). In this method a stereo microscope is used to determine the number of individual vessels occurring in three 5 mm 2 circles. The mean number of vessels per mm2 was then calculated. To determine the number of uniseriate, bi­ seriate and multiseriate rays (where multi­ seriate is ~ 3-seriate) 100 rays were examined in taQgentiallongitudinal sections. The proportion of vessel, fibre, axial pa­ renchyma and ray tissue was measured for each sample using a 25 point grid on ten random areas of a transverse section. This number of sampling points was chosen so as -----~-~------400 to give an accuracy of measurement of 5% at the 0.05 level. The presence of crystals was determined Fig. 1. Diagram of eastern Australia showing from radial longitudinal sections using polar­ sampling locations, latitude and state boun­ ised light microscopy. A classification system daries (Q = Queensland, N = New South was developed for the purpose of this study: Wales, V = Victoria, T = Tasmania). crystals were recorded as being absent, rare (0-0.1 mm-2), moderately abundant (0.1-1 mm-2) and abundant (> 1 mm-2). The presence or absence of parenchyma samples) or Tasmania (14 samples) as shown bands was determined by examination under in Figure 1. To reduce the effect of juvenile low power incident light on freshly cut trans­ wood, stems smaller than 10 cm diameter verse surfaces. were excluded from this study. Standard errors and least significant dif­ Wood anatomical properties measured in­ ferences were calculated. The 0.05 level was clude: vessel lumen diameter, vessel member used in significance tests. length, vessel frequency, percentage of uni-, bi- and multi seriate rays, percentage of vari­ ous cell types (vessels, axial parenchyma, Results rays and fibres), abundance of crystals and Results of measurements are shown in presence of parenchyma bands. In addition, Table 1. The small number of New South methanol extracted wood basic density was Wales and Victorian samples makes inter­ determined in samples from Queensland and preting some of the results from these two Tasmania. states more difficult. However, as differences Vessel lumen diameter and vessel member can be seen between the number of crystals, length were measured using a Leitz projection vessel frequency and the percentage of ray microscope and digitising board. The tan­ tissue present in samples from New South gential diameter of 50 vessel lumens was Wales and Victoria (Table I), it was con­ measured from the projected image of a trans­ sidered inappropriate to pool the results from verse section. Average maximum, average these two states. minimum and mean diameter were then cal­ Mean vessel diameter was significantly culated for each sample. The length (in­ larger in Queensland samples rather than Tas­ cluding tails) of 20 vessel members was manian samples (Table 1; Figs. 2-4). Mean measured from a projected image of the mac­ vessel diameter was also greater in samples erated wood and the mean vessel member from Queensland when these were compared length was then calculated. to pooled samples from the other states.

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Table 1. Results of measurement of wood anatomical properties. These are expressed either as a mean or a percent of the total number of samples for that state. Standard errors are shown in brackets. Underline indicates no significant difference (0.05 level) between adjacent states deter­ mined using least significant differences (not shown for the presence of crystals or parenchyma bands due to the method of measurement).

Queensland New South Wales Victoria Tasmania

Sample size 9 6 4 14

Vessel diameter (J.IlD) maximum (average) 217 (11) 204 (15) 198 (16) 198 (9) ------minimum (average) 31 (5) 22 (2) 23 (3) 27 (4) ------mean 135 (6) 114 (6) 124 (12) 120 (5)

Vessel frequency (mm-2) 7.53 (0.66) 6.47 (0.34) 4.60 (1.20) 5.50 (0.52)

Mean vessel member 151 (6) 179 (11) length (J.IlD)

Ray width (%) uniseriate 67 (3) 55 (8) 63 (13) 52 (5)

biseriate 31 (3) 31 (4) 32 (10) 37 (3)

multiseriate 2 (1) 15 (5) 5 (3) 11 (3)

Cell types (%) vessels 14 (1) 11 (1) 11 (3) 9 (1)

parenchyma 11 (1) 7 (1) 9 (2) 6 (1)

rays 10 (1) 13 (2) 8 (1) 10 (1)

fibres 65 (1) 71 (3) 72 (4) 75 (1)

Crystals (%) absent 0 33 75 100 rare 13 0 25 0 moderately abundant 38 50 0 0 abundant 50 17 0 0

Parenchyma bands (% of 25 33 0 50 samples with bands)

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0.12,------.

IZZI Queensland _ Tasmania 0.10

0.08

;>. g 0.06 ~ ~ 0.04

0.02

I~ IIFlP.R.. n o • 50- 100- 150- 200- 250- 60 110 160 210 260 Vessel diameter (!-Im)

Fig. 2. Frequency histogram of vessel diameter for samples from Queensland and Tasmania.

Vessel frequency was significantly greater in Discussion the northern states and vessel member length Increasing latitude is generally associated was found to be significantly greater in Tas­ with cooler temperatures. In eastern Australia mania. Queensland samples had a significant­ latitude also has important hydrological rami­ ly greater proportion of vessels and paren­ fications. Although the mean rainfall between chyma than that found in other states and a states is similar, in the southern areas cold icy significantly lower percentage of fibres than winters and dry summers may result in water that of Tasmanian samples. The proportion stress particularly during the summer growth of uniseriate rays was significantly lower in period. For this reason Tasmania can be con­ Tasmania and the percentage of multiseriate sidered to be a more xeric environment than rays was lower in Queensland. Bands of pa­ Queensland. The observed trend towards de­ renchyma were most frequently Qbserved in creasing vessel diameter with increasing dry­ samples from Tasmania. ness and latitude is generally in agreement As latitude increased there was a progres­ with the findings of previous studies for sive decrease in the number of crystals pres­ other species and genera (Baas 1973; Van der ent. All samples from Queensland had crys­ Graaff & Baas 1974; Van den Oever et al. tals present and no crystals were observed in 1981; Baas et al. 1983; Ford 1984; Dickison Tasmanian samples. & Phend 1985; Baas 1986). Although an ex­ Extracted wood basic density was not sig­ ception to this has been reported by Den nificantly different between Queensland and Outer and Van Veenendaal (1976) who found Tasmanian samples. Mean basic density be­ greater vessel diameter in species from drier ing 521 (S.D.± 40) kg m-3 and 495 (S.D.± savanna areas when undertaking a compar­ 85) kg m-3 respectively. ison with rain forest species.

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Figs. 3 & 4. Transverse section of a wood sample of Acacia melanoxylon from Queensland (3) and Tasmania (4). Scale bar = 100 J.I1Il.

Vessel diameter can also be considered in Vessel dimorphism occurred in all states terms of the frequency distribution of dia­ but was more pronounced in samples from meters (Fig. 2). In both Queensland and Tas­ Tasmania (Fig. 2), where there was a distinct manian samples the greatest proportion of increase in the proportion of vessels having vessel diameters are between 130 and 140 smaller diameters (from 10-60 11m). Vessel 11m; however, Queensland samples have the dimorphism may provide conductive mech­ highest proportion of vessels with a diameter anisms which would still remain functional of 120 11m or greater. Vessel dimorphism after large vessels are disabled (Carlquist was greater in samples from Tasmania. Ves­ 1985). Thus, the greater degree of vessel di­ sel diameter frequency distributions for New morphism in Tasmanian samples may pro­ South Wales and Victoria were found to be vide a higher level of vessel safety and an intermediate between Queensland and Tas­ adaptive advantage to more extreme water mania. stress. Narrower vessels, although less efficient The decrease of vessel frequency and in­ for water conduction, are regarded as safer in crease in vessel member length found with drier environments since they allow the de­ increasing latitude appears to be unusual velopment of greater negative pressures be­ (Baas 1973; Van den Oever et al. 1981; Baas fore embolisms form and cause loss of func­ et al. 1983; Dickison & Phend 1985). Shorter tion to the vessel (Zimmermann 1983; Baas vessel member lengths have been suggested 1986). Queensland with a more humid cli­ as an advantage in xeric environments be­ mate and wetter summers, had a higher pro­ cause they may give greater strength to the portion of wider vessels, thus potentially vessel wall allowing it to withstand greater providing greater efficiency in an area where negative pressures during water stress (Carl­ transpirational requirements and water availa­ quist 1977). Furthermore, the greater number bility are higher. of recesses associated with shorter vessel

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members have been proposed as allowing in samples from Tasmania. However, the embolisms to be more easily trapped. How­ absence of parenchyma bands in Victorian ever, the first of these suggestions has been samples and the occurrence in samples from criticised as not allowing for parallel trends Queensland and New South Wales makes in mesic-xeric and tropical-temperate-arctic any association with latitude uncertain. Larg­ series and the second hypothesis is said to er sample sizes are necessary to clearly show require experimental confirmation (Baas et al. a trend which may be associated with lati­ 1983). The observed positive relationship be­ tude. tween vessel member length and increasingly The presence of crystals appeared to be xeric environmental conditions could suggest strongly negatively related to latitude. An ex­ support for the view (Baas et al. 1983; Zim­ amiation of anatomical data from 4000 spe­ mermann 1983) that vessel member length is cies showed that 31 % of species with larger of little or no adaptive significance in A. me­ vessel diameters (> 200 !tm, n = 564) have lanoxylon. Alternately, as trees have greater crystals present (in ordinary cells) while only vessel member lengths than shrubs (Baas et 24% of species with small vessel diameters al. 1983) the increase in vessel member « 50 !tm, n = 1094) have crystals. In A. length may be accounted for by variation in melanoxylon as vessel diameter decreases the species habit, trees of A. melanoxylon with latitude an associated decrease in the reaching their greatest development in Tas­ abundance of crystals is consistent with these mania. Genetic variation may also be a con­ findings. However, environmental factors tributing factor. other than those associated with latitude have Since vessel width, frequency and per­ been shown to influence the development of centage of vessel tissue decrease with latitude crystals (Umemoto & Hozumi 1972) and in A. melanoxylon, the potential for water these or genetic factors could be responsible conduction may also decrease. Flow through for the trend observed. vessels is proportional to the fourth power of Farrell and Ashton (1978) observed that vessel diameter (Zimmermann 1983); there­ A. me/anoxylon seedling germination times fore a decrease in total vessel conduction and various leaf parameters such as rachis would occur with increasing latitude unless length were associated with seed source and very large (and unlikely) increases in sap­ climate. They found morphological variation wood area occur. The apparent decrease in over the geographical range was continuous conducting ability with latitude may be asso­ rather than stepped. The results of the present ciated with lower transpirational demands in study suggest a similar gradation of wood the cooler southern areas in contrast to those anatomical characters over the species range. which may occur in the north. However, the degree to which phenotypic The overall proportion of ray tissue ap­ plasticity and genotype are reponsible for the peared unaffected by latitude; however, the anatomical variation found across the latitu­ proportion of uniseriate rays was significant­ dinal range of this species is still to be deter­ ly less in Tasmania and the percentage of mined. multi seriate rays was lower in Queensland. For uniseriate rays this is the opposite from Conclusions what was found in Styracaceae by Dickison In eastern Australia various features of the and Phend (1985), but is in agreement with wood anatomy of A. melanoxy/on were re­ their findings for multiseriate rays. The con­ lated to increasing latitude (and the associated sistency of the trends shown between states increase in xeric conditions). A positive rela­ in Table 1 suggests that, in A. melanoxylon, tionship occurred between latitude and each ray seriateness is correlated with latitude. of vessel member length, proportion of fibres There was a large amount of variance in the and multiseriate rays. Correlations were neg­ proportion of uniseriate and biseriate rays in ative between latitude and vessel frequency, Victoria, probably due to the small number of vessel diameter, the abundance of crystals samples from this state. and the proportion of: uniseriate rays, vessels Bands of parenchyma were more frequent and axial parenchyma.

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Proportion of ray tissue and basic density Farrell, T.P. & D.H. Ashton. 1978. Popula­ was not found to be correlated with latitude. tion studies on Acacia melanoxylon R.Br. Further study is required to determine if the I. Variation in seed and vegetative charac­ presence of parenchyma bands is positively teristics. Aust. 1 Bot. 26: 365-379. associated with latitude. Ford, 1 1984. Vessel characteristics of the Increasing latitude appeared to be asso­ wood anatomy of some Australian species ciated with wood anatomical features con­ of Acacia in relation to habit. Proc. Pacif. sistent with increased safety from vessel em­ Regional Wood Anat. Conf., Tsukuba, bolism, decreased vessel efficiency and lower Japan (ed. S. Sudo): 156-158. transpirational demand. Graaff, N.A. van der & P. Baas. 1974. Wood anatomical variation in relation to References latitude and altitude. Blumea 22: 101-121. Baas, P. 1973. The wood anatomy of Hex Lanyon, lW. 1981. Card key for the identi­ (Aquifoliaceae) and its ecological and phy­ fication of the commercial timbers used in logenetic significance. Blumea 21: 193- New South Wales. For. Comm. N.S.W. 258. (Aust.) research note No. 40. - 1986. Ecological patterns in xylem anat­ Metcalfe, C. R. & L. Chalk. 1950. Anatomy omy. In: On the economy of plant fonn of the dicotyledons. Clarendon Press, Ox­ and function (ed. T.l Givnish): 327- ford. 352. Cambridge Univ. Press, Cambridge, Oever, L. van den, P. Baas & M. Zandee. New York. 1981. Comparative wood anatomy of - ,E. Werker & A. Fahn. 1983. Some eco­ Symplocos and latitude and altitude of logical trends in vessel characters. IAWA provenance. IAWA Bull. n.s. 2: 3-24. Bull. n.s. 4: 141-159. Outer, R.w. den & W.L.H. van Veenendaal. Boland, D.l, M.I.H. Brooker, G.M. Chip­ 1976. Variation in wood anatomy of spe­ pendale, N. Hall, B.P.M. Hyland, R.D. cies with a distribution covering both rain Johnston, D.A. Kleinig & lD. Turner. forest and savanna areas of the Ivory 1985. Forest trees of Australia. CSIRO, Coast, West Africa. In: Wood structure in Melbourne. biological and technological research (eds. Carlquist, S.1977.Ecological factors in wood P. Baas, A.l Bolton & D.M. Catling): evolution: a floristic approach. Amer. J. 182-195. Leiden Bot. Series, Leiden Uni­ Bot. 64: 887-896. versity Press, The Hague. - 1985. Observations on functional wood Pedley, L. 1986. Derivation and dispersal of histology of vines and lianas: vessel Acacia (Leguminosae), with particular ref­ dimorphism, tracheids, vasicentric tra­ erence to Australia, and the recognition of cheids, narrow vessels, and parenchyma. Senegalia and Racospenna. Bot. J. Linn. Aliso 11: 139-157. Soc. 92: 219-254. Dadswell, H.E. & A.M. Eckersley. 1935. Robbertse, P.J., G. Venter & H. Janse van The identification of the principal com­ Rensburg. 1980. The wood anatomy of mercial Australian timbers other than euca­ the South African Acacias. lAWA Bull. lypts. CSIR (Aust.) Bull. No. 90. n.s. 1: 93-103. Dickison, W.C. & K.D. Phend. 1985. Wood Umemoto, K. & K. Hozumi. 1972. Correla­ anatomy of the Styracaceae: evolutionary tion between the degree of air pollution and ecological considerations.IAW A Bull. and the distribution of calcium oxalate n. s. 6: 3-22. crystals in the ginkgo leaf. Microchem. 1 Fahn, A., E. Werker & P. Baas. 1986. Wood 17: 689-702. anatomy and identification of trees and Zimmennann, M.H. 1983. Xylem structure shrubs from Israel and adjacent regions. and the ascent of sap. Springer, Berlin, Israel Acad. Sci. & Human., Jerusalem. Heidelberg, New York.

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