- Email: [email protected]
Permeability of poplar normal wood and tension wood bioincised by Physisporinus vitreus and Xylaria longipes
International Biodeterioration & Biodegradation 105 (2015) 178e184
Contents lists available at ScienceDirect
International Biodeterioration & Biodegradation journal homepage: www.elsevier.com/locate/ibiod
Short communication
Permeability of poplar normal wood and tension wood bioincised by Physisporinus vitreus and Xylaria longipes Mohammad Emaminasab*, Asghar Tarmian, Kambiz Pourtahmasi Department of Wood and Paper Science & Technology, Faculty of Natural Resources, University of Tehran, Karaj, Islamic Republic of Iran
a r t i c l e i n f o
a b s t r a c t
Article history: Received 26 November 2014 Received in revised form 6 September 2015 Accepted 7 September 2015 Available online 21 September 2015
Bioincising impacts of white-rot fungus, Physisporinus vitreus and soft-rot fungus, Xylaria longipes on the porous structure and radial permeability of poplar normal wood and tension wood were studied. Fungal cultivation was performed in an incubator at 25 C and 85% relative humidity for 15, 30 and 45 days. Fracture of pectin-rich gelatinous layer of tension wood occurred due to incubation with P. vitreus. However, a simultaneous degradation in the cell walls and middle lamellae was observed. Both fungi had negative effects on the permeability, probably due to blocking of fluid flow paths by the fungal hyphae. Reduction in the permeability was more remarkable with P. vitreus. Our results showed that the role of Glayer containing fibers can be neglected for radial permeability of tension wood. Overall, such fungal bioincising techniques cannot be considered as successful approaches to improve the permeability of tension wood. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Bioincising fungus Permeability Poplar Physisporinus vitreus Tension wood Xylaria longipes
1. Introduction Treatability of wood with various gas or liquid preservatives varies depending on its permeability. Wood permeability may change to a great extent due to its structure variation. Tension wood is an abnormal tissue that typically develops in fast-growing trees, such as poplars. It is usually found on the upper side of leaning stems (Cunderlik et al., 1992; Ruelle, 2014). Tension wood is undesirable for wood preservation because it reduces the wood permeability. The permeability of beech tension wood was reported to be lower than that of its corresponding normal wood due to changes in the vessel properties (Tarmian and Perre, 2009). Different mechanical, chemical and biological techniques were used to improve the permeability of refractory woods (Schwarze et al., 2006; Thaler et al., 2012; Dashti et al., 2012; Ramezanpour et al., 2014). Recently, a bioincising technique with Physisporinus vitreus, a white-rot fungus has been developed to increase the permeability of Norway spruce (Schwarze and Landmesser, 2000; Schwarze et al., 2006; Lehringer et al., 2010; Thaler et al., 2012). As a result, a selective delignification of tracheid walls and
* Corresponding author. E-mail address: [email protected] (M. Emaminasab). http://dx.doi.org/10.1016/j.ibiod.2015.09.003 0964-8305/© 2015 Elsevier Ltd. All rights reserved.
degradation of pectin-rich pit membranes occur and are associated with bore holes, cavities and notches in the walls (Schmidt et al., 1997; Schwarze and Landmesser, 2000). However, by increasing the incubation time, the bordered pits and tracheid walls are strongly degraded (Lehringer et al., 2010). It was claimed that isolates of P. vitreus have an extraordinary capacity to induce permeability changes in the heartwood of Norway spruce and silver fir without significant strength loss (Schwarze et al., 2006). Xylaria is a genus of ascomycetous fungi that commonly forms typical soft-rot cavities in wood (Nilsson et al., 1989). It can be considered as a selective fungus because the middle lamella is not attacked by this type II soft rot. Pectins and xyloglucans appear to be good candidates for the origin of gel structure of gelatinous layer (G-layer) in tension wood. The G-layer is mostly composed of large cellulose macrofibrils, with large overall porosity. The pores are likely filled with pectins and arabinogalactan proteins (AGPs) (Fagerstedt et al., 2014). Although Norway spruce is one of the most economically important coniferous species in Europe, the use of fast-growing species, such as poplar has been increased for some outdoor applications where high mechanical strength is not required. Poplar wood has low natural durability, but can be protected from decay by applying chemical preservatives. In contrast to poplar sapwood, the heartwood is difficult to treat. However, according to EN 350-2 (1994), the species exhibits an unusual high level of variability. It
M. Emaminasab et al. / International Biodeterioration & Biodegradation 105 (2015) 178e184
becomes more difficult to treat because of wetwood or tension wood formation (Ward, 1986; Tarmian and Perre, 2009). The main objective of the present study was to investigate the effects of bioincising fungi, P. vitreus and Xylaria longipes on the tension wood of poplar (Populus nigra). 2. Material and methods 2.1. Specimen preparation Freshly cut boards of poplar (P. nigra) containing tension wood were used. The tension wood was detected on the cross section with the aid of Herzberg reagent (Badia et al., 2005) and anatomical studies. The air dried boards with dimensions of 15 25 50 mm3 were cut for permeability measurements according to EN 113 (2004). Specimens with dimensions of 20 20 60 mm3 were prepared for measuring compression strength parallel to grain according to ISO 3787. The strength was measured before and after fungal cultivation. Five repetitions were used for each treatment. 2.2. Fungal isolation and purification The fruit body of X. longipes was collected from decomposing wood bark in north forest of Iran located in Guilan Province. For molecular verification of the fungal species, pure cultures obtained from the fruit body were identified by rDNA-ITS analysis according to Schmidt et al. (2012). Fungal DNA was extracted, amplified by polymerase chain reaction (PCR) of the ITS region and sequenced. Identification was done by sequence comparison with sequences deposited in the DNA databases using BLAST program (Bari, 2014). Pure fungal cultures were maintained on malt extract agar in Petri dishes. P. vitreus was prepared from University of Hamburg in Germany. 2.3. Fungal cultivation The oven dried (103 C, 24 h) and steam sterilized (20 min, 121 C, 1.5 bar) specimens were exposed to white rot fungus (P. vitreus) and soft rot fungus (X. longipes) according to EN 113 procedure (2004). The specimens were positioned on glass bases above malt extract agar (MEA) in petri dishes. Fungal cultivation was performed in an incubator at 25 C and 85% relative humidity for 15, 30 and 45 days (Fig. 1). After incubation, specimens were
179
isolated, cleaned of mycelia by scalpel and their mass loss was measured. 2.4. Anatomical studies 45-day incubated specimens were used for anatomical studies by using Scanning Electron Microscope and bright-field light microscope. For light microscopy, transverse and radial sections of 10e15 mm thickness were cut with a sliding microtome. The sections were then stained with 0.5% safranineastra blue. Four replicates were used for each treatment and six fields were studied per each replicate. For SEM, moist cubic blocks were prepared by sliding microtome and then dried for 18 h at 50 C. 2.5. Air permeability measurement Cylindrical samples with 18 mm in diameter and 15 mm in length were used for permeability measurement. After moisture conditioning to 12%, the lateral surfaces of samples were coated by epoxy resin to limit airflow through the radial direction. Radial gas permeability was measured by the falling-water displacement method (Siau, 1995) using the apparatus shown in Fig. 2 (Taghiyari et al., 2010). A superficial permeability coefficient was then calculated by Siau's equations (Siau, 1995):
kg ¼
VdCLðPatm 0:074ZÞ 0:76mHg tAð0:074ZÞðPatm 0:037ZÞ 1:013 106 Pa
C ¼1þ
Vrð0:074DZÞ VdðPatm 0:074ZÞ
(1)
(2)
where Kg is longitudinal specific permeability (m3 m1), Vd ¼ p r2Dz [r ¼ radius of measuring tube (m)] (m3), C is correction factor for gas expansion as a result of change in static head and viscosity of water, L is length of wood specimen (m), Patm is atmospheric pressure (m Hg), z is average height of water over surface of reservoir during period of measurement (m), t is time (s), A is crosssectional area of wood specimen (m2), Dz is change in height of water during time t (m) and Vr is total volume of apparatus above point 1 (including volume of hoses) (m3). 2.6. Liquid permeability test Five control and incubated samples at moisture content of 12% were impregnated with safranin solution (Sano et al., 2005) by the process shown in Fig. 3. Before impregnation, the samples were end coated by epoxy resin to avoid the penetration along the longitudinal direction. After impregnation, the samples were cut in the middle. The pattern of safranin penetration was then studied using a stereo microscope. The images were taken and analyzed by Image J software. 2.7. Statistical analysis Statistical analysis was performed with SPSS software. Duncan multiple range test (DMRT) was applied to test the statistical significance at a ¼ 0.05 level. 3. Results and discussion
Fig. 1. A schematic view of samples in culture medium. A. Compression strength sample (20 20 60 mm3); B. Liquid permeability sample (15 25 50 mm3); C. Air permeability sample (15 25 50 mm3); D. Glass base; E. Culture medium; F. Petri dish.
3.1. Changes in the wood structure As shown in Fig. 4, the bioincising fungi had different effects on the structure of poplar normal and tension wood. X. longipes
180
M. Emaminasab et al. / International Biodeterioration & Biodegradation 105 (2015) 178e184
Fig. 2. The permeability measurement device.
middle lamellae and cell walls was caused by X. longipes (Fig. 4c and 4d). The fungal hyphae can be seen within the vessel lumina, intervessel and intervessel-ray pits (Fig. 5). 3.2. Mass loss and compression strength
Fig. 3. Diagram of impregnation method.
degraded the wood structure in a greater extent than P. vitreus. Fractures in gelatinous layer of tension wood were observed as a result of incubation by P. vitreus (Fig. 4f). The cell walls and middle lamellae were slightly degraded by the fungus. Our results are in agreement with those of Schwarze et al. (2006) who reported hydrolysis of bordered pit membranes by P. vitreus. In contrast to our results, Blanchette et al. (1994) found that Trametes versicolor had no remarkable damage on the gelatinous layer of tension wood in Populus tremuloides and Acer rubrum. A significant degradation of
Mass loss of all specimens was under 7% after 45 days of incubation. The mass loss was increased by increasing the incubation period from 15 to 45 days (Table 1). Mass losses of tension wood and normal wood were almost similar. X. longipes caused a larger mass loss in both tension and normal wood than did P. vitreus. The mass loss with X. longipes varied between 0.9 and 6.8%, and with P. vitreus between 0.7 and 5.7%. Lehringer et al. (2010) reported a mass loss of 1.3% for Norway spruce after five-week incubation by P. vitreus. Thaler et al. (2012) found a mass loss under 3.6% for Norway spruce exposed to soft-rot fungus (Hypoxylon fragiforme) for 45 days. The authors also indicated that the mass loss significantly increased by increasing the incubation time. Compression strength of specimens reduced significantly with increasing the incubation time (Table 1). Tension wood exhibited a larger strength reduction than normal wood. After 45-day incubation by P. vitreus, the strength decreased by about 12 and 21% for normal wood and tension wood, respectively. The strength reduction was even higher with X. longipes, ranged from 41 to 51%, probably due to the larger mass loss. This can be explained by the fact that X. longipes degrades the cell walls and middle lamellae in a greater extent than P. vitreus. The compression strength is provided by lignin (Walker, 1993). The
M. Emaminasab et al. / International Biodeterioration & Biodegradation 105 (2015) 178e184
181
Fig. 4. Light microscope, transverse sections of control (a and b) and bioincised samples (c, d, e and f) after 45 days of incubation. a.: Normal wood. b.: Tension wood. c.: Degradation of middle lamellae with Xylaria longipes in normal wood, d.: Degradation of middle lamellae with Xylaria longipes in tension wood, e.: Degradation of cell cavity from inside by Physiporinus vitreus in normal wood. f.: Fracture of gelatinous layer by Physiporinus vitreus in tension wood.
lignin content of middle lamellae is about 70e75%. Thus, the main reason for reduction in the strength is the degradation of middle lamellae. Thaler et al. (2012) also found a significant decrease in the compression strength of Norway spruce exposed to Antrodia vaillantii and Hypoxylon fragiforme after 30 days of incubation. However, Schwarze et al. (2006) reported that reduction in the impact bending strength of the species was negligible after six weeks of incubation by P. vitreus. These contradictory findings could be the result of different fungal exposure conditions used in each study. 3.3. Permeability Both fungi had negative effects on the air permeability of poplar wood (Table 1), perhaps due to blocking of fluid flow paths by the fungal hyphae (Fig. 5). The difference between control and incubated wood was observed to be greater after 45 days of incubation. Tension wood exhibited a smaller permeability reduction compared to normal wood. The permeability reduction was greater with P. vitreus than with X. longipes, probably due to greater volume of P. vitreus hyphae inside the porous structure of wood. After 45 days of incubation, the reduction varied from 47 to 77% with X. longipes, and from 74 to 119% with P. vitreus. Vessels are the main fluid transfer paths in hardwoods, and the permeability of wood is significantly influenced by their anatomical features (Kurjatko et al., 2006). The function of inter-vessel pits is radial fluid transport from one vessel to another and pit membranes are responsible for at least 50% of the total hydraulic resistance in a plant (Choat € lltt€ et al., 2008; Ho a, 2011). Although G-layer in tension wood was broken down by P. vitreus, no improvement was observed in the wood permeability. Thus, it can be claimed that the radial permeability of tension wood is controlled by ray parenchyma and intervessel pits rather than G-layer containing fibers. Tarmian and
Perre (2009) also reported that the low permeability of beech tension wood in radial direction can be related to the small intervessel pits. A relatively small number of pits in tension wood may also affect the radial permeability. In contrast to our results, permeability improvement in softwoods by the fungal incubation was reported in previous studies (Schwarze et al., 2006; Thaler et al., 2012). Lehringer (2011) showed that the longitudinal gas permeability of Norway spruce heartwood was significantly increased after 3, 5, 7 and 9 weeks of incubation with P. vitreus. Green and Clausen (1999) also reported that pinewood treatment with white and brown rot fungi increased its longitudinal gas permeability. There was good agreement between the two methods of permeability measurements. Liquid permeability measurements showed that the penetration of safranin through the radial direction of incubated specimens significantly decreased by increasing the incubation period (Fig. 6 and Table 2). There was no pronounced difference in the liquid permeability of control and 15day incubated samples, whereas remarkable difference was observed for longer incubation period. According to previous works, the environmental growth condition has a pronounced influence on the mechanism of P. vitreus colonizing on Norway spruce. The speed and homogeneity of substrate colonization and the selectivity of fungal activity towards pit membrane degradation are determined by the incubation parameters (Lehringer, 2011). Thaler et al. (2012) also showed that prolonged pre-treatment periods of Norway spruce with bioincising fungi (Antrodia vaillantii, Hypoxylon fragiforme and Sclerophoma pithyophila) from 30 days to 45 days did not improve the treatability but resulted in more prominent losses of mechanical properties. The authors claimed that one possible reason for this reduction is the blocking of voids between cells by fungal mycelia, resulting in the limited liquid penetration.
182
M. Emaminasab et al. / International Biodeterioration & Biodegradation 105 (2015) 178e184
Fig. 5. SEM images, radial section of samples bioincised with Physiporinus vitreus and Xylaria longipes after 45 days of incubation, a.: blocking of vessel lumina by Xylaria longipes hypha (Arrow) in normal wood. b.: blocking of vessels lumina by Physiporinus vitreus hypha (Arrow) in normal wood. c.: blocking of vessel-ray pits by Xylaria longipes hypha (Arrow) in tension wood d.: blocking of vessel-ray pits by Physiporinus vitreus hypha (Arrow) in tension wood.
Table 1 Influence of fungal incubation on the mass loss, permeability and compression strength of poplar normal and tension wood. Fungi
Kind of wood species
Physisporinus vitreus Normal wood
Xylaria longipes
Control
Time of Average mass Average permeability Average compression Average permeability Avergae compression exposure (day) loss (%) [ (1016(m2)] strength (MoR) [N mm2] reduction (%) strength reduction (%)
15 30 45 Tension wood 15 30 45 Normal wood 15 30 45 Tension wood 15 30 45 Normal wood e Tension wood e
0.7 2.3 4.7 1 3.2 5.7 1 3.3 6.8 0.9 3.4 6.8 e e
(0.3)a (0.9)b (0.7)c (0.3)a (0.6)b (0.8)c (0.2)a (1.2)b (2)d (0.2)a (1.5)b (1.5)d
99 77 50 100 85 63 101 94 62 98 92 75 109 110
(7)cd (19)abcd (6)a (15)cd (23)bcd (15)ab (8)cd (40)bcd (2)ab (14)cd (45)bcd (18)abc (22)cd (36)d
15.2 15.6 15.1 16.2 15.8 14.9 15.3 14.5 11.9 15.8 14.6 11.9 16.8 18.1
(0.7)bc (0.5)bc (0.1)bc (1)bcd (0.6)bc (1.7)bc (0.5)bc (0.6)b (0.4)a (1)bc (0.6)bc (2.6)a (0.4)cd (0.8)d
10 43 119 10 30 74 8 17 77 13 20 47 e e
11 8 12 12 15 21 10 16 41 15 24 51 e e
The same letter in the same column indicates no significant difference at the 95% confidence interval.
4. Conclusion Although short term incubation of Norway spruce wood with P. vitreus was claimed to be a biotechnological approach for
improving the permeability of this refractory species with negligible loss of wood strength, this technique still needs to be optimized for other wood species. The growth control of this bioincising fungus is complex. Therefore, the fungus can increase
M. Emaminasab et al. / International Biodeterioration & Biodegradation 105 (2015) 178e184
Fig. 6. Treatability pattern of control and bioincised specimens by safranin. Scale: 4 mm. N.: Normal wood. T.: Tension wood. P.: Physiporinus vitreus. X.: Xylaria longipes.
183
184
M. Emaminasab et al. / International Biodeterioration & Biodegradation 105 (2015) 178e184
Table 2 Penetration depth of safranin through control and bioincised normal and tension wood. Fungi
Wood type
Time of exposure (day)
Average minimum penetration depth (mm)
Physisporinus vitreus
Normal wood
15 30 45 15 30 45 15 30 45 15 30 45 e e
4.6 2.8 1.5 4.4 4.4 1.5 4.3 3.7 2.2 4.2 3.3 2.6 5.5 5.3
Tension wood
Xylaria longipes
Normal wood
Tension wood
Control
Normal wood Tension wood
(0.1)cde (0.5)abc (0.5)a (2.1)bcde (1)cde (0.4)a (0.1)bcde (0.6)bcde (0.1)ab (1.7)bcde (1.6)abcd (0.6)abc (0.9)e (1.4)de
Average maximum penetration depth (mm) 6.4 5.3 4 7.7 5.7 3.3 6.1 5.4 3.5 7.4 5.2 4.3 7.7 7.6
(0.2)defg (1.9)abcde (2)abc (0.8)g (0.4)bcdefg (1.8)a (0.4)cdefg (0.3)abcdef (0.6)ab (0.7)efg (1)abcde (1.6)abcd (0.5)fg (1.1)g
Saturated area (%) 84de 66bc 40a 79bcde 70bcd 38a 82cde 65b 45a 75bcde 62b 41a 91e 91e
The same letter in the same column indicates no significant difference at the 95% confidence interval.
the wood permeability under certain incubation conditions. However, it is questionable whether such bioincising techniques are able to improve the treatability class of refractory wood species and allow them to be moderately easy treated according to EN 350-2 (1994). Our results showed that neither P. vitreus nor X. longipes selectively degrade the pectin-rich gelatinous layer of tension wood and a simultaneous degradation in the cell walls and middle lamellae can be occurred. This non-selective degradation was also reported in previous studies for Norway spruce, suggesting the optimization of incubation parameters. Neither P. vitreus nor X. longipes enhanced the tension wood permeability. On the whole, it can be concluded that the radial permeability of poplar tension wood is not controlled by the G-layer containing fiber cells. Acknowledgments Authors would like to thank Dr. Hamid Reza Taghiyari, Prof. Dr. Olaf Schmidt and Dr. Ali Naghi Karimi for preparing Physisporinus vitreus fungi. References Badia, M.A., Mothe, F., Constant, T., Nepveu, G., 2005. Assessment of tension wood detection based on shiny appearance for three poplar cultivars. Ann. For. Sci. 62, 43e49. Bari, E., 2014. Potential of Biological Degradation of Oriental Beech Wood by the White-rot Fungus Pleurotus Ostreatus and the Effects on its Mechanical and Chemical Properties and Comparison with the Standard White-rot Fungus Trametes versicolor. MSc dissertation. Sari Agriculture and Natural Resources University, Sari, Iran. Blanchette, R.A., Obst, J.R., Timell, T.E., 1994. Biodegradation of compression wood and tension wood by white and brown rot fungi. Holzforsch. Int. J. Biol. Chem. Phys. Technol. Wood 48, 34e42. Choat, B., Cobb, A.R., Jansen, S., 2008. Structure and function of bordered pits: new discoveries and impacts on whole-plant hydraulic function xylem. New Phytol. 177, 608e625. Cunderlik, I., Kudela, J., Molinski, w, 1992. Reaction beech wood in drying process. In: IUFRO Drying Conference, Vienna, pp. 350e353. Dashti, H., Tarmian, A., Faezipour, M., Shahverdi, M., 2012. Effect of microwave radiation and pre-steaming treatments on the conventional drying characteristics of Fir wood (Abies alba l.). Lignocellulose 1, 166e173. EN 113, 2004. Wood Preservatives e Test Method for Determining the Protective Effectiveness Against Wood Destroying Basidiomycetes e Determination of the Toxic Values. CEN Eur. Comm. Stand. EN 350-2, 1994. Durability of Wood and Wood-based Products-natural Durability of Solid Wood-Part 2: Guide to Natural Durability and Treatability of Selected Wood Species of Importance in Europe. Fagerstedt, K.V., Mellerowicz, E., Gorshkova, T., Ruel, K., Joseleau, J.-P., 2014. Cell wall €€ polymers in reaction Wood. In: Gardiner, B., Barnett, J., Saranpa a, P., Gril, J. (Eds.), The Biology of Reaction Wood. Springer Series in Wood Science, Springer Berlin Heidelberg, pp. 37e106.
Green, F., Clausen, C.A., 1999. Production of polygalacturonase and increase of longitudinal gas permeability in southern pine by brown-rot and white-rot fungi. Holzforschung 53, 563e568. €lltta €, T., 2011. A carbon costegain model explains the observed patterns of xyle Ho safety and efficiency. Plant Cell Environ. 34, 1819e1834. ISO 3787, Wood e tests methods e determination of ultimate stress in compression parallel to grain. Kurjatko, S., Mamonova, M., Babiak, M., Hudec, J., 2006. Permeability of ash and elm wood for water. In: Kurjatko, Stanislav, Kudela, Jozef, Lagana, Rastislav (Eds.), Wood structure and Properties '06. Arbora Publishers, Zvolen, Slovakia, pp. 281e287. Lehringer, C., 2011. Permeability Improvement of Norway Spruce Wood with the € ttingen White Rot Fungus Physisporinus Vitreus. Georg-August-University, Go (PhD thesis). Lehringer, C., Hillebrand, K., Richter, K., Arnold, M., Schwarze, F.W., Militz, H., 2010. Anatomy of bioincised Norway spruce wood. Int. Biodeterior. Biodegrad. 64, 346e355. Nilsson, T., Daniel, G., Kirk, K., Obst, J.R., 1989. Chemistry and microscopy of wood decay by some higher ascomycetes. Holzforschung 43, 11e18. Ramezanpour, M., Tarmian, A., Taghiyari, H.R., 2014. Improving impregnation properties of fir wood to acid copper chromate (ACC) with microwave pretreatment. iForest (Early View) e1ee6 [online 2014-04-01] URL: http://www. sisef.it/iforest/contents/?. id¼ifor1119-007. Ruelle, J., 2014. Morphology, anatomy and ultrastructure of reaction Wood. In: €a €, P., Gril, J. (Eds.), The Biology of Reaction Wood. Gardiner, B., Barnett, J., Saranpa Springer Series in Wood Science, Springer Berlin Heidelberg, pp. 13e35. Schmidt, O., Schmitt, U., Moreth, U., Potsch, T., 1997. Wood decay by the whiterotting basidiomycete Physisporinus vitreus from a cooling tower. Holzforschung 51, 193e200. Schmidt, O., Gaiser, O., Dujesiefken, D., 2012. Molecular identification of decay fungi in the wood of urban trees. Eur. J. For. Res. 131, 885e891. Schwarze, F.W., Landmesser, H., 2000. Preferential degradation of pit membranes within tracheids by the basidiomycete Physisporinus vitreus. Holzforschung 54, 461e462. Schwarze, F.W., Landmesser, H., Zgraggen, B., Heeb, M., 2006. Permeability changes in heartwood of Picea abies and Abies alba induced by incubation with Physisporinus vitreus. Holzforschung 60, 450e454. Sano, Y., Okamura, Y., Utsumi, Y., 2005. Visualizing water-conduction pathways of living trees: selection of dyes and tissue preparation methods. Tree Physiol. 25, 269e275. Siau, J.F., 1995. Wood: Influence of Moisture on Physical Properties. Department of Wood Science and Forest Products Virginian Polytechnic Institute and State University, Blacksburg, VA, pp. 1e63. Taghiyari, H.R., Karimi, A.N., Parsapajouh, D., Pourtahmasi, K., 2010. Study on the longitudinal gas permeability of juvenile wood and mature wood. Special topic and reviews in porous media. Begell House Prod. 1, 345e351. Tarmian, A., Perre, P., 2009. Air permeability in longitudinal and radial directions of compression wood of Picea abies L. and tension wood of Fagus sylvatica L. Holzforschung 63, 352e356. Thaler, N., Lesar, B., Kari z, M., Humar, M., 2012. Bioincising of Norway spruce wood using wood inhabiting fungi. Int. Biodeterior. Biodegrad. 68, 51e55. Walker, J.C.F., 1993. Basic wood chemistry and cell wall ultrastructure. In: Walker, J.C.F. (Ed.), Primary Wood Processing, Principles and Practice. Chapman and Hall, London, pp. 23e67. Ward, J.C., 1986. The effect of wetwood on lumber drying times and rates: an exploratory evaluation with longitudinal gas permeability. Wood Fiber Sci. 18, 288e307.
Contents lists available at ScienceDirect
International Biodeterioration & Biodegradation journal homepage: www.elsevier.com/locate/ibiod
Short communication
Permeability of poplar normal wood and tension wood bioincised by Physisporinus vitreus and Xylaria longipes Mohammad Emaminasab*, Asghar Tarmian, Kambiz Pourtahmasi Department of Wood and Paper Science & Technology, Faculty of Natural Resources, University of Tehran, Karaj, Islamic Republic of Iran
a r t i c l e i n f o
a b s t r a c t
Article history: Received 26 November 2014 Received in revised form 6 September 2015 Accepted 7 September 2015 Available online 21 September 2015
Bioincising impacts of white-rot fungus, Physisporinus vitreus and soft-rot fungus, Xylaria longipes on the porous structure and radial permeability of poplar normal wood and tension wood were studied. Fungal cultivation was performed in an incubator at 25 C and 85% relative humidity for 15, 30 and 45 days. Fracture of pectin-rich gelatinous layer of tension wood occurred due to incubation with P. vitreus. However, a simultaneous degradation in the cell walls and middle lamellae was observed. Both fungi had negative effects on the permeability, probably due to blocking of fluid flow paths by the fungal hyphae. Reduction in the permeability was more remarkable with P. vitreus. Our results showed that the role of Glayer containing fibers can be neglected for radial permeability of tension wood. Overall, such fungal bioincising techniques cannot be considered as successful approaches to improve the permeability of tension wood. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Bioincising fungus Permeability Poplar Physisporinus vitreus Tension wood Xylaria longipes
1. Introduction Treatability of wood with various gas or liquid preservatives varies depending on its permeability. Wood permeability may change to a great extent due to its structure variation. Tension wood is an abnormal tissue that typically develops in fast-growing trees, such as poplars. It is usually found on the upper side of leaning stems (Cunderlik et al., 1992; Ruelle, 2014). Tension wood is undesirable for wood preservation because it reduces the wood permeability. The permeability of beech tension wood was reported to be lower than that of its corresponding normal wood due to changes in the vessel properties (Tarmian and Perre, 2009). Different mechanical, chemical and biological techniques were used to improve the permeability of refractory woods (Schwarze et al., 2006; Thaler et al., 2012; Dashti et al., 2012; Ramezanpour et al., 2014). Recently, a bioincising technique with Physisporinus vitreus, a white-rot fungus has been developed to increase the permeability of Norway spruce (Schwarze and Landmesser, 2000; Schwarze et al., 2006; Lehringer et al., 2010; Thaler et al., 2012). As a result, a selective delignification of tracheid walls and
* Corresponding author. E-mail address: [email protected] (M. Emaminasab). http://dx.doi.org/10.1016/j.ibiod.2015.09.003 0964-8305/© 2015 Elsevier Ltd. All rights reserved.
degradation of pectin-rich pit membranes occur and are associated with bore holes, cavities and notches in the walls (Schmidt et al., 1997; Schwarze and Landmesser, 2000). However, by increasing the incubation time, the bordered pits and tracheid walls are strongly degraded (Lehringer et al., 2010). It was claimed that isolates of P. vitreus have an extraordinary capacity to induce permeability changes in the heartwood of Norway spruce and silver fir without significant strength loss (Schwarze et al., 2006). Xylaria is a genus of ascomycetous fungi that commonly forms typical soft-rot cavities in wood (Nilsson et al., 1989). It can be considered as a selective fungus because the middle lamella is not attacked by this type II soft rot. Pectins and xyloglucans appear to be good candidates for the origin of gel structure of gelatinous layer (G-layer) in tension wood. The G-layer is mostly composed of large cellulose macrofibrils, with large overall porosity. The pores are likely filled with pectins and arabinogalactan proteins (AGPs) (Fagerstedt et al., 2014). Although Norway spruce is one of the most economically important coniferous species in Europe, the use of fast-growing species, such as poplar has been increased for some outdoor applications where high mechanical strength is not required. Poplar wood has low natural durability, but can be protected from decay by applying chemical preservatives. In contrast to poplar sapwood, the heartwood is difficult to treat. However, according to EN 350-2 (1994), the species exhibits an unusual high level of variability. It
M. Emaminasab et al. / International Biodeterioration & Biodegradation 105 (2015) 178e184
becomes more difficult to treat because of wetwood or tension wood formation (Ward, 1986; Tarmian and Perre, 2009). The main objective of the present study was to investigate the effects of bioincising fungi, P. vitreus and Xylaria longipes on the tension wood of poplar (Populus nigra). 2. Material and methods 2.1. Specimen preparation Freshly cut boards of poplar (P. nigra) containing tension wood were used. The tension wood was detected on the cross section with the aid of Herzberg reagent (Badia et al., 2005) and anatomical studies. The air dried boards with dimensions of 15 25 50 mm3 were cut for permeability measurements according to EN 113 (2004). Specimens with dimensions of 20 20 60 mm3 were prepared for measuring compression strength parallel to grain according to ISO 3787. The strength was measured before and after fungal cultivation. Five repetitions were used for each treatment. 2.2. Fungal isolation and purification The fruit body of X. longipes was collected from decomposing wood bark in north forest of Iran located in Guilan Province. For molecular verification of the fungal species, pure cultures obtained from the fruit body were identified by rDNA-ITS analysis according to Schmidt et al. (2012). Fungal DNA was extracted, amplified by polymerase chain reaction (PCR) of the ITS region and sequenced. Identification was done by sequence comparison with sequences deposited in the DNA databases using BLAST program (Bari, 2014). Pure fungal cultures were maintained on malt extract agar in Petri dishes. P. vitreus was prepared from University of Hamburg in Germany. 2.3. Fungal cultivation The oven dried (103 C, 24 h) and steam sterilized (20 min, 121 C, 1.5 bar) specimens were exposed to white rot fungus (P. vitreus) and soft rot fungus (X. longipes) according to EN 113 procedure (2004). The specimens were positioned on glass bases above malt extract agar (MEA) in petri dishes. Fungal cultivation was performed in an incubator at 25 C and 85% relative humidity for 15, 30 and 45 days (Fig. 1). After incubation, specimens were
179
isolated, cleaned of mycelia by scalpel and their mass loss was measured. 2.4. Anatomical studies 45-day incubated specimens were used for anatomical studies by using Scanning Electron Microscope and bright-field light microscope. For light microscopy, transverse and radial sections of 10e15 mm thickness were cut with a sliding microtome. The sections were then stained with 0.5% safranineastra blue. Four replicates were used for each treatment and six fields were studied per each replicate. For SEM, moist cubic blocks were prepared by sliding microtome and then dried for 18 h at 50 C. 2.5. Air permeability measurement Cylindrical samples with 18 mm in diameter and 15 mm in length were used for permeability measurement. After moisture conditioning to 12%, the lateral surfaces of samples were coated by epoxy resin to limit airflow through the radial direction. Radial gas permeability was measured by the falling-water displacement method (Siau, 1995) using the apparatus shown in Fig. 2 (Taghiyari et al., 2010). A superficial permeability coefficient was then calculated by Siau's equations (Siau, 1995):
kg ¼
VdCLðPatm 0:074ZÞ 0:76mHg tAð0:074ZÞðPatm 0:037ZÞ 1:013 106 Pa
C ¼1þ
Vrð0:074DZÞ VdðPatm 0:074ZÞ
(1)
(2)
where Kg is longitudinal specific permeability (m3 m1), Vd ¼ p r2Dz [r ¼ radius of measuring tube (m)] (m3), C is correction factor for gas expansion as a result of change in static head and viscosity of water, L is length of wood specimen (m), Patm is atmospheric pressure (m Hg), z is average height of water over surface of reservoir during period of measurement (m), t is time (s), A is crosssectional area of wood specimen (m2), Dz is change in height of water during time t (m) and Vr is total volume of apparatus above point 1 (including volume of hoses) (m3). 2.6. Liquid permeability test Five control and incubated samples at moisture content of 12% were impregnated with safranin solution (Sano et al., 2005) by the process shown in Fig. 3. Before impregnation, the samples were end coated by epoxy resin to avoid the penetration along the longitudinal direction. After impregnation, the samples were cut in the middle. The pattern of safranin penetration was then studied using a stereo microscope. The images were taken and analyzed by Image J software. 2.7. Statistical analysis Statistical analysis was performed with SPSS software. Duncan multiple range test (DMRT) was applied to test the statistical significance at a ¼ 0.05 level. 3. Results and discussion
Fig. 1. A schematic view of samples in culture medium. A. Compression strength sample (20 20 60 mm3); B. Liquid permeability sample (15 25 50 mm3); C. Air permeability sample (15 25 50 mm3); D. Glass base; E. Culture medium; F. Petri dish.
3.1. Changes in the wood structure As shown in Fig. 4, the bioincising fungi had different effects on the structure of poplar normal and tension wood. X. longipes
180
M. Emaminasab et al. / International Biodeterioration & Biodegradation 105 (2015) 178e184
Fig. 2. The permeability measurement device.
middle lamellae and cell walls was caused by X. longipes (Fig. 4c and 4d). The fungal hyphae can be seen within the vessel lumina, intervessel and intervessel-ray pits (Fig. 5). 3.2. Mass loss and compression strength
Fig. 3. Diagram of impregnation method.
degraded the wood structure in a greater extent than P. vitreus. Fractures in gelatinous layer of tension wood were observed as a result of incubation by P. vitreus (Fig. 4f). The cell walls and middle lamellae were slightly degraded by the fungus. Our results are in agreement with those of Schwarze et al. (2006) who reported hydrolysis of bordered pit membranes by P. vitreus. In contrast to our results, Blanchette et al. (1994) found that Trametes versicolor had no remarkable damage on the gelatinous layer of tension wood in Populus tremuloides and Acer rubrum. A significant degradation of
Mass loss of all specimens was under 7% after 45 days of incubation. The mass loss was increased by increasing the incubation period from 15 to 45 days (Table 1). Mass losses of tension wood and normal wood were almost similar. X. longipes caused a larger mass loss in both tension and normal wood than did P. vitreus. The mass loss with X. longipes varied between 0.9 and 6.8%, and with P. vitreus between 0.7 and 5.7%. Lehringer et al. (2010) reported a mass loss of 1.3% for Norway spruce after five-week incubation by P. vitreus. Thaler et al. (2012) found a mass loss under 3.6% for Norway spruce exposed to soft-rot fungus (Hypoxylon fragiforme) for 45 days. The authors also indicated that the mass loss significantly increased by increasing the incubation time. Compression strength of specimens reduced significantly with increasing the incubation time (Table 1). Tension wood exhibited a larger strength reduction than normal wood. After 45-day incubation by P. vitreus, the strength decreased by about 12 and 21% for normal wood and tension wood, respectively. The strength reduction was even higher with X. longipes, ranged from 41 to 51%, probably due to the larger mass loss. This can be explained by the fact that X. longipes degrades the cell walls and middle lamellae in a greater extent than P. vitreus. The compression strength is provided by lignin (Walker, 1993). The
M. Emaminasab et al. / International Biodeterioration & Biodegradation 105 (2015) 178e184
181
Fig. 4. Light microscope, transverse sections of control (a and b) and bioincised samples (c, d, e and f) after 45 days of incubation. a.: Normal wood. b.: Tension wood. c.: Degradation of middle lamellae with Xylaria longipes in normal wood, d.: Degradation of middle lamellae with Xylaria longipes in tension wood, e.: Degradation of cell cavity from inside by Physiporinus vitreus in normal wood. f.: Fracture of gelatinous layer by Physiporinus vitreus in tension wood.
lignin content of middle lamellae is about 70e75%. Thus, the main reason for reduction in the strength is the degradation of middle lamellae. Thaler et al. (2012) also found a significant decrease in the compression strength of Norway spruce exposed to Antrodia vaillantii and Hypoxylon fragiforme after 30 days of incubation. However, Schwarze et al. (2006) reported that reduction in the impact bending strength of the species was negligible after six weeks of incubation by P. vitreus. These contradictory findings could be the result of different fungal exposure conditions used in each study. 3.3. Permeability Both fungi had negative effects on the air permeability of poplar wood (Table 1), perhaps due to blocking of fluid flow paths by the fungal hyphae (Fig. 5). The difference between control and incubated wood was observed to be greater after 45 days of incubation. Tension wood exhibited a smaller permeability reduction compared to normal wood. The permeability reduction was greater with P. vitreus than with X. longipes, probably due to greater volume of P. vitreus hyphae inside the porous structure of wood. After 45 days of incubation, the reduction varied from 47 to 77% with X. longipes, and from 74 to 119% with P. vitreus. Vessels are the main fluid transfer paths in hardwoods, and the permeability of wood is significantly influenced by their anatomical features (Kurjatko et al., 2006). The function of inter-vessel pits is radial fluid transport from one vessel to another and pit membranes are responsible for at least 50% of the total hydraulic resistance in a plant (Choat € lltt€ et al., 2008; Ho a, 2011). Although G-layer in tension wood was broken down by P. vitreus, no improvement was observed in the wood permeability. Thus, it can be claimed that the radial permeability of tension wood is controlled by ray parenchyma and intervessel pits rather than G-layer containing fibers. Tarmian and
Perre (2009) also reported that the low permeability of beech tension wood in radial direction can be related to the small intervessel pits. A relatively small number of pits in tension wood may also affect the radial permeability. In contrast to our results, permeability improvement in softwoods by the fungal incubation was reported in previous studies (Schwarze et al., 2006; Thaler et al., 2012). Lehringer (2011) showed that the longitudinal gas permeability of Norway spruce heartwood was significantly increased after 3, 5, 7 and 9 weeks of incubation with P. vitreus. Green and Clausen (1999) also reported that pinewood treatment with white and brown rot fungi increased its longitudinal gas permeability. There was good agreement between the two methods of permeability measurements. Liquid permeability measurements showed that the penetration of safranin through the radial direction of incubated specimens significantly decreased by increasing the incubation period (Fig. 6 and Table 2). There was no pronounced difference in the liquid permeability of control and 15day incubated samples, whereas remarkable difference was observed for longer incubation period. According to previous works, the environmental growth condition has a pronounced influence on the mechanism of P. vitreus colonizing on Norway spruce. The speed and homogeneity of substrate colonization and the selectivity of fungal activity towards pit membrane degradation are determined by the incubation parameters (Lehringer, 2011). Thaler et al. (2012) also showed that prolonged pre-treatment periods of Norway spruce with bioincising fungi (Antrodia vaillantii, Hypoxylon fragiforme and Sclerophoma pithyophila) from 30 days to 45 days did not improve the treatability but resulted in more prominent losses of mechanical properties. The authors claimed that one possible reason for this reduction is the blocking of voids between cells by fungal mycelia, resulting in the limited liquid penetration.
182
M. Emaminasab et al. / International Biodeterioration & Biodegradation 105 (2015) 178e184
Fig. 5. SEM images, radial section of samples bioincised with Physiporinus vitreus and Xylaria longipes after 45 days of incubation, a.: blocking of vessel lumina by Xylaria longipes hypha (Arrow) in normal wood. b.: blocking of vessels lumina by Physiporinus vitreus hypha (Arrow) in normal wood. c.: blocking of vessel-ray pits by Xylaria longipes hypha (Arrow) in tension wood d.: blocking of vessel-ray pits by Physiporinus vitreus hypha (Arrow) in tension wood.
Table 1 Influence of fungal incubation on the mass loss, permeability and compression strength of poplar normal and tension wood. Fungi
Kind of wood species
Physisporinus vitreus Normal wood
Xylaria longipes
Control
Time of Average mass Average permeability Average compression Average permeability Avergae compression exposure (day) loss (%) [ (1016(m2)] strength (MoR) [N mm2] reduction (%) strength reduction (%)
15 30 45 Tension wood 15 30 45 Normal wood 15 30 45 Tension wood 15 30 45 Normal wood e Tension wood e
0.7 2.3 4.7 1 3.2 5.7 1 3.3 6.8 0.9 3.4 6.8 e e
(0.3)a (0.9)b (0.7)c (0.3)a (0.6)b (0.8)c (0.2)a (1.2)b (2)d (0.2)a (1.5)b (1.5)d
99 77 50 100 85 63 101 94 62 98 92 75 109 110
(7)cd (19)abcd (6)a (15)cd (23)bcd (15)ab (8)cd (40)bcd (2)ab (14)cd (45)bcd (18)abc (22)cd (36)d
15.2 15.6 15.1 16.2 15.8 14.9 15.3 14.5 11.9 15.8 14.6 11.9 16.8 18.1
(0.7)bc (0.5)bc (0.1)bc (1)bcd (0.6)bc (1.7)bc (0.5)bc (0.6)b (0.4)a (1)bc (0.6)bc (2.6)a (0.4)cd (0.8)d
10 43 119 10 30 74 8 17 77 13 20 47 e e
11 8 12 12 15 21 10 16 41 15 24 51 e e
The same letter in the same column indicates no significant difference at the 95% confidence interval.
4. Conclusion Although short term incubation of Norway spruce wood with P. vitreus was claimed to be a biotechnological approach for
improving the permeability of this refractory species with negligible loss of wood strength, this technique still needs to be optimized for other wood species. The growth control of this bioincising fungus is complex. Therefore, the fungus can increase
M. Emaminasab et al. / International Biodeterioration & Biodegradation 105 (2015) 178e184
Fig. 6. Treatability pattern of control and bioincised specimens by safranin. Scale: 4 mm. N.: Normal wood. T.: Tension wood. P.: Physiporinus vitreus. X.: Xylaria longipes.
183
184
M. Emaminasab et al. / International Biodeterioration & Biodegradation 105 (2015) 178e184
Table 2 Penetration depth of safranin through control and bioincised normal and tension wood. Fungi
Wood type
Time of exposure (day)
Average minimum penetration depth (mm)
Physisporinus vitreus
Normal wood
15 30 45 15 30 45 15 30 45 15 30 45 e e
4.6 2.8 1.5 4.4 4.4 1.5 4.3 3.7 2.2 4.2 3.3 2.6 5.5 5.3
Tension wood
Xylaria longipes
Normal wood
Tension wood
Control
Normal wood Tension wood
(0.1)cde (0.5)abc (0.5)a (2.1)bcde (1)cde (0.4)a (0.1)bcde (0.6)bcde (0.1)ab (1.7)bcde (1.6)abcd (0.6)abc (0.9)e (1.4)de
Average maximum penetration depth (mm) 6.4 5.3 4 7.7 5.7 3.3 6.1 5.4 3.5 7.4 5.2 4.3 7.7 7.6
(0.2)defg (1.9)abcde (2)abc (0.8)g (0.4)bcdefg (1.8)a (0.4)cdefg (0.3)abcdef (0.6)ab (0.7)efg (1)abcde (1.6)abcd (0.5)fg (1.1)g
Saturated area (%) 84de 66bc 40a 79bcde 70bcd 38a 82cde 65b 45a 75bcde 62b 41a 91e 91e
The same letter in the same column indicates no significant difference at the 95% confidence interval.
the wood permeability under certain incubation conditions. However, it is questionable whether such bioincising techniques are able to improve the treatability class of refractory wood species and allow them to be moderately easy treated according to EN 350-2 (1994). Our results showed that neither P. vitreus nor X. longipes selectively degrade the pectin-rich gelatinous layer of tension wood and a simultaneous degradation in the cell walls and middle lamellae can be occurred. This non-selective degradation was also reported in previous studies for Norway spruce, suggesting the optimization of incubation parameters. Neither P. vitreus nor X. longipes enhanced the tension wood permeability. On the whole, it can be concluded that the radial permeability of poplar tension wood is not controlled by the G-layer containing fiber cells. Acknowledgments Authors would like to thank Dr. Hamid Reza Taghiyari, Prof. Dr. Olaf Schmidt and Dr. Ali Naghi Karimi for preparing Physisporinus vitreus fungi. References Badia, M.A., Mothe, F., Constant, T., Nepveu, G., 2005. Assessment of tension wood detection based on shiny appearance for three poplar cultivars. Ann. For. Sci. 62, 43e49. Bari, E., 2014. Potential of Biological Degradation of Oriental Beech Wood by the White-rot Fungus Pleurotus Ostreatus and the Effects on its Mechanical and Chemical Properties and Comparison with the Standard White-rot Fungus Trametes versicolor. MSc dissertation. Sari Agriculture and Natural Resources University, Sari, Iran. Blanchette, R.A., Obst, J.R., Timell, T.E., 1994. Biodegradation of compression wood and tension wood by white and brown rot fungi. Holzforsch. Int. J. Biol. Chem. Phys. Technol. Wood 48, 34e42. Choat, B., Cobb, A.R., Jansen, S., 2008. Structure and function of bordered pits: new discoveries and impacts on whole-plant hydraulic function xylem. New Phytol. 177, 608e625. Cunderlik, I., Kudela, J., Molinski, w, 1992. Reaction beech wood in drying process. In: IUFRO Drying Conference, Vienna, pp. 350e353. Dashti, H., Tarmian, A., Faezipour, M., Shahverdi, M., 2012. Effect of microwave radiation and pre-steaming treatments on the conventional drying characteristics of Fir wood (Abies alba l.). Lignocellulose 1, 166e173. EN 113, 2004. Wood Preservatives e Test Method for Determining the Protective Effectiveness Against Wood Destroying Basidiomycetes e Determination of the Toxic Values. CEN Eur. Comm. Stand. EN 350-2, 1994. Durability of Wood and Wood-based Products-natural Durability of Solid Wood-Part 2: Guide to Natural Durability and Treatability of Selected Wood Species of Importance in Europe. Fagerstedt, K.V., Mellerowicz, E., Gorshkova, T., Ruel, K., Joseleau, J.-P., 2014. Cell wall €€ polymers in reaction Wood. In: Gardiner, B., Barnett, J., Saranpa a, P., Gril, J. (Eds.), The Biology of Reaction Wood. Springer Series in Wood Science, Springer Berlin Heidelberg, pp. 37e106.
Green, F., Clausen, C.A., 1999. Production of polygalacturonase and increase of longitudinal gas permeability in southern pine by brown-rot and white-rot fungi. Holzforschung 53, 563e568. €lltta €, T., 2011. A carbon costegain model explains the observed patterns of xyle Ho safety and efficiency. Plant Cell Environ. 34, 1819e1834. ISO 3787, Wood e tests methods e determination of ultimate stress in compression parallel to grain. Kurjatko, S., Mamonova, M., Babiak, M., Hudec, J., 2006. Permeability of ash and elm wood for water. In: Kurjatko, Stanislav, Kudela, Jozef, Lagana, Rastislav (Eds.), Wood structure and Properties '06. Arbora Publishers, Zvolen, Slovakia, pp. 281e287. Lehringer, C., 2011. Permeability Improvement of Norway Spruce Wood with the € ttingen White Rot Fungus Physisporinus Vitreus. Georg-August-University, Go (PhD thesis). Lehringer, C., Hillebrand, K., Richter, K., Arnold, M., Schwarze, F.W., Militz, H., 2010. Anatomy of bioincised Norway spruce wood. Int. Biodeterior. Biodegrad. 64, 346e355. Nilsson, T., Daniel, G., Kirk, K., Obst, J.R., 1989. Chemistry and microscopy of wood decay by some higher ascomycetes. Holzforschung 43, 11e18. Ramezanpour, M., Tarmian, A., Taghiyari, H.R., 2014. Improving impregnation properties of fir wood to acid copper chromate (ACC) with microwave pretreatment. iForest (Early View) e1ee6 [online 2014-04-01] URL: http://www. sisef.it/iforest/contents/?. id¼ifor1119-007. Ruelle, J., 2014. Morphology, anatomy and ultrastructure of reaction Wood. In: €a €, P., Gril, J. (Eds.), The Biology of Reaction Wood. Gardiner, B., Barnett, J., Saranpa Springer Series in Wood Science, Springer Berlin Heidelberg, pp. 13e35. Schmidt, O., Schmitt, U., Moreth, U., Potsch, T., 1997. Wood decay by the whiterotting basidiomycete Physisporinus vitreus from a cooling tower. Holzforschung 51, 193e200. Schmidt, O., Gaiser, O., Dujesiefken, D., 2012. Molecular identification of decay fungi in the wood of urban trees. Eur. J. For. Res. 131, 885e891. Schwarze, F.W., Landmesser, H., 2000. Preferential degradation of pit membranes within tracheids by the basidiomycete Physisporinus vitreus. Holzforschung 54, 461e462. Schwarze, F.W., Landmesser, H., Zgraggen, B., Heeb, M., 2006. Permeability changes in heartwood of Picea abies and Abies alba induced by incubation with Physisporinus vitreus. Holzforschung 60, 450e454. Sano, Y., Okamura, Y., Utsumi, Y., 2005. Visualizing water-conduction pathways of living trees: selection of dyes and tissue preparation methods. Tree Physiol. 25, 269e275. Siau, J.F., 1995. Wood: Influence of Moisture on Physical Properties. Department of Wood Science and Forest Products Virginian Polytechnic Institute and State University, Blacksburg, VA, pp. 1e63. Taghiyari, H.R., Karimi, A.N., Parsapajouh, D., Pourtahmasi, K., 2010. Study on the longitudinal gas permeability of juvenile wood and mature wood. Special topic and reviews in porous media. Begell House Prod. 1, 345e351. Tarmian, A., Perre, P., 2009. Air permeability in longitudinal and radial directions of compression wood of Picea abies L. and tension wood of Fagus sylvatica L. Holzforschung 63, 352e356. Thaler, N., Lesar, B., Kari z, M., Humar, M., 2012. Bioincising of Norway spruce wood using wood inhabiting fungi. Int. Biodeterior. Biodegrad. 68, 51e55. Walker, J.C.F., 1993. Basic wood chemistry and cell wall ultrastructure. In: Walker, J.C.F. (Ed.), Primary Wood Processing, Principles and Practice. Chapman and Hall, London, pp. 23e67. Ward, J.C., 1986. The effect of wetwood on lumber drying times and rates: an exploratory evaluation with longitudinal gas permeability. Wood Fiber Sci. 18, 288e307.