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Cell wall properties of softwood deteriorated by fungi: combined chemical analyses, FT-IR spectroscopy, nanoindentation and micromechanical modelling
2013 - IRG/WP 13-20527
Mechanical properties of wood are determined by its inherent hierarchical microstructure, starting at the nanometer scale, where the elementary components cellulose, hemicelluloses, and lignin build up the wood cell wall material. Fungi cause degradation and decomposition of these components and, thus, alter the mechanical properties of wood. The aim of this study is to gain new insight into these relationships at the cell wall level, particularly at early stages of degradation characterized by a mass loss of less than 10 %. Early detection of deterioration is essential during monitoring of timber structures as it may help avoiding subsequent larger scale damages. This contribution presents results of an ambitious experimental programme covering the determination of earlywood/latewood specific compositional data with consistent microstructural and micromechanical properties. Scots pine (Pinus sylvestris L.) sapwood was studied in reference condition and after degradation by brown rot (Gloeophyllum trabeum) and white rot (Trametes versicolor), respectively. Ultrastructural and compositional data were acquired by means of FT IR spectroscopy and wet chemical analyses. Micro-structural features such as the microfibril angle were determined by X-ray diffraction. Mechanical properties of sound and degraded wood cell walls were determined using nanoindentation, yielding the (anisotropic) indentation modulus of the S2 cell wall layer and the cell corner middle lamella of Scots pine tracheids. Aiming at the identification of relationships between ultrastructural and micromechanical characteristics, two different approaches were followed. On the one hand, multivariate data analysis was applied. On the other hand, a multiscale micromechanical model was used to derive causal relationships between structure and (mechanical) function for deteriorated wood. Anisotropic indentation theory allows calculating model predictions for the indentation modulus of the S2 cell wall layer based on measured chemical compositions resulting from the degradation process. Comparing these predictions with the experimental results enables to test hypotheses on possible scenarios of wood cell wall deterioration during fungal attack. Identified relationships between ultrastructural, microstructural, and micromechanical characteristics will be discussed as well as the potential of micromechanical modelling in the analysis of fungal degradation strategies and their effect on the mechanical behaviour.
L Wagner, T K Bader, K de Borst, T Ters, K Fackler


Ultra-structural observations on the degradation of wood surfaces during weathering
1987 - IRG/WP 2280
Radiata pine (Pinus radiata D. Don) sapwood was converted into blocks with a transverse face about 5 mm square and measuring 8 mm longitudinally. Transverse (T.S.), Radial (R.L.S.) and Tangential (T.L.S.) surfaces were prepared and specimens exposed to the weather inclined at 45° facing equatorially for periods of between 20-60 days. After 30 days exposure erosion of the middle lamella was observed followed after 40 days exposure by extensive separation of individual fibres at the interface of the middle lamella and secondary wall. Degradation of the S2 layer of the cell wall revealed corrugations orientated parallel to the fibre axis suggesting preferential removal of cell wall components. Further degradation proceeded by progressive delamination and checking of the S2 and erosion of the S3 cell wall layer. In addition to the above changes preferential degradation of the rays was observed in radial (R.L.S.) and tangential (T.L.S.) longitudinal surfaces.
P D Evans, S Thein


Resistance of Alstonia scholaris vestures to degradation by tunnelling bacteria
1992 - IRG/WP 92-1547
Electron microscopic examination of vessels and fibre-tracheids in the wood of Alstonia scholaris exposed to tunnelling bacteria (TB) in a liquid culture showed degradation of all areas of the secondary wall. The highly lignified middle lamella was also degraded in advanced stages of TB attack. However, vestured pit membranes and vestures appeared to be resistant to degradation by TB even when other wall areas in Alstonia scholaris wood cells were severely degraded. The size comparison indicated vestures to be considerably smaller than TB, and we suspect that this may primarily be the reason why vestures in Alstonia scholaris wood were found to be resistant to degradation by TB.
A P Singh, T Nilsson, G F Daniel


Ultrastructural observations on wood-degrading erosion bacteria
1986 - IRG/WP 1283
G F Daniel, T Nilsson


Water-based water repellents for treatment of wood
1987 - IRG/WP 3446
The water uptake by wood can be reduced by treatment with a water repellent. The water repellents most commonly used are solvent based. In the present work a new type of water repellent that is water-based has been investigated. Two different treatments have shown an effect of the same order as a commercial solvent based product. The cellular distribution of the water repellents has been investigated and for one of the formulations a more uniform distribution can be seen at the impregnated surface. Use of water as a solvent would be advantageous due to lower cost and non-toxicity.
I G Svensson, G Hägglund, I Johansson, W B Banks


Degradation of the normal fibre walls of rubberwood (Hevea brasiliensis) by the tropical blue-stain fungus Botryodiplodia theobromae
1998 - IRG/WP 98-10286
Rubberwood was examined by light microscopy and transmission electron microscopy (TEM) after exposure to the common tropical sapstain fungus Botryodiplodia theobromae for four weeks to study hyphal colonisation of wood cells and to determine if this fungus also degraded lignified normal fibre cell walls in addition to the walls of non-lignified elements. Light microscopy revealed relatively large diameter hyphae to be abundantly present in parenchyma cells. The hyphae were also present in other types of wood cells, including fibres. TEM provided evidence of fibre wall degradation in the normal rubberwood in the form of lumen wall erosion (type-2 soft rot decay). These observations suggest that the ability of B. theobromae to degrade lignified wood cells walls should be viewed with concern when utilising rubberwood which has been severely sapstained, particularly after prolonged exposure to this fungus.
A A H Wong, A P Singh


Ultrastructural aspects of bacterial attacks on an archaeological wood
1993 - IRG/WP 93-10007
Transmission electron microscopy of wood from a Chinese ship submerged in the mud for over 900 years showed bacteria to be the main factor for its deterioration. The micromorphology of degraded wood cell walls was similar to that observed during the attacks of wood by erosion bacteria. Other bacterial forms, previously considered lo be scavenging bacteria, were also abundant in degraded areas of the wall. The observations on the breakdown of the waterlogged archaeological wood are discussed in context with the available information on bacterial degradation of wood under near-anaerobic conditions.
Yoon Soo Kim, A P Singh


The Relationship of Fiber Cell Wall Ultrastructure to Soft Rot Decay in Kempas (Koompassia malaccensis) Heartwoo
2004 - IRG/WP 04-10541
The ultrastructure of fiber walls in kempas (koompassia malaccensis) heartwood was examined in relation to soft rot cavity formation. The fibers consisted of middle lamella and thick secondary wall. The secondary wall was differentiated in to a S1 layer, and a unique multi-lamellar S2 layer. Two distinct forms of lamellae were recognisable, one type being considerably thicker than the other. They also differed in their electron density, the thin lamellae being much denser than the thick lamellae. It was not possible to determine whether a S3 layer also existed, because of the presence of a dense material coating the lumen wall, which obscured the definition of this region of the fiber wall. The resistance to soft rot varied with different regions of the fiber wall, middle lamella being completely resistant and the thick S2 lamellae least resistant. The observed relationship between the ultrastructure of these fiber wall regions and the degree of their resistance/susceptibility to soft rot cavity formation is discussed.
A P Singh, A H H Wong, Yoon Soo Kim, Seung-Gon Wi


Estimation of effective diffusion path lengths in wood by swelling studies
1989 - IRG/WP 3524
The effective average distance that a solute must diffuse to penetrate the cell wall matrix following pressure treatment is estimated from the rate of swelling of wood, vacuum treated with water. It is assumed that the diffusion paths are similar for water and a solute such as a wood preservative component. Since bound water diffusion coefficients for water in wood have been estimated by others, the effective path lengths (Le) can be estimated. Effective average path lengths are estimated for red pine (Pinus resinosa), Southern yellow pine (Pinus sp), trembling aspen (Populus tremuloides) and soft maple (Acer rubra) sapwood and red oak (Quercus rubra) heartwood samples. The estimated path lengths are shortest for the softwoods, and longest for the ring porous oak. The results reflect the different patterns of cell penetration and different densities of the wood species.
P A Cooper, R Churma


The attack of naturally durable and creosote treated timbers by Limnoria tripunctata Menzies
1995 - IRG/WP 95-10132
Limnoria tripunctata was found tunnelling in creosote treated Douglas fir (Pseudotsuga menziesii) pilings and naturally durable greenheart (Ocotea rodiaei) gate seals at two sites on the south coast of the United Kingdom. Examination of thc creosote-treated wood showed that Limnoria tunnels were concentrated at a depth of 2-3 cm from the timber surface, where creosote loading was lower. Fewer tunnels occured in the heavily creosoted outer zone. Sections through Limnoria tunnels in wood fixed on site were examined using the scanning electron microscope (SEM). These studies showed that S2 layers of wood cell walls adjacent to Limnoria tunnels were decayed by tunnelling bacteria in many cases. Examination of greenheart seals showed that Limnoria tunnelled to a depth of 1.5 cm, in the soft-rot decay zone. The heads of the Limnoria tunnels also penetrated "sound" wood to a depth of 2 cm. Examination of sections through Limnoria tunnels showed that wood cells adjacent to tunnels were decayed by both soft-rot fungi and tunnelling bacteria. In addition, a range of prokaryotes and protoctists were attached to tunnel walls in this instance. The size of bitemarks along the tunnel walls suggested Limnoria would ingest a range of these micro-organisms along with the wood substrate. Gut contents of Limnoria fixed at both sites were screened for microorganisms using the SEM. This study failed to show micro-organisms on the surface of wood particles during gut transit, which suggested that ingested microbes were digested by Limnoria.
A J Pitman, G S Sawyer, G F Daniel


Role of cell wall structure in soft rot decay of bamboo
1995 - IRG/WP 95-10133
Models of soft rot hyphal penetration of bamboo cell walls are proposed. Soft rot hyphae show an interesting capability of penetrating the bamboo cell wall in different forms; typical longitudinal penetrating hyphae and tangentially orientated penetrating hyphae. The second form of penetration was found to be different from that normally associated with wood cell walls. The differences can be attributed to the cell wall structure of bamboo. Soft rot hyphae normally follow the microfibrillar orientation in either the broad lamellae or the narrow lamellae in bamboo cell walls. Hyphae that grow in the broad lamellae normally penetrate in the longitudinal direction and follow the orientation of the microfibrils of this layer of the cell wall. This produces a 'typical' longitudinal penetrating hyphae and cavity. Soft rot hyphae are also found penetrating in the tangential direction. These arise from radially orientated hyphae trying to penetrate across the lamellated cell wall neighbouring cells. When a radially orientated hyphae encounters the narrow lamellae, the hyphae can reorientate in the direction of the microfibrils in this lamellae. Thus, the hyphae penetrate in a tangential direction in the cell wall. These types of penetrations are not seen in wood cell walls.
O Sulaiman, R J Murphy


Ultrastructure of degraded, CCA-treated Pinus radiata wood from a marine pile
1990 - IRG/WP 1461
During an inspection of marine piles, 12 years after installation, severe degradation was noted on one of them in the vicinity of a corroded eye-bolt. The wood was dark brown in colour and tended to crumble easily. Wood fragments were examined by light microscopy and scanning and transmission electron microscopy and were also analysed for carbohydrates and lignin. Light microscopy showed numerous cracks in tracheid walls resulting in delamination at middle lamella - S1 and S1 - S2 junctures and also in fractures across the tracheid wall. Chemical analysis showed extensive losses in hemicelluloses and also losses in cellulose. Observations with polarised light microscopy supported the data from chemical analysis on cellulose degradation. Although presence of microbial flora in the lumen of wood cells was revealed by scanning electron microscopy, transmission electron microscopy showed only occasional soft rot decay zones in the S2 layer. We suggest that the degradation of Pinus radiata wood cell wall is primarily due to chemical attack, fungal decay playing a minor role.
A P Singh, M E Hedley


Degradation of the gelatinous-layer in aspen and rubber wood by the blue stain fungus Lasiodiplodia theobromae
1996 - IRG/WP 96-10168
Studies on the degradative ability of the blue stain fungus Lasiodiplodia theobromae Pat. have shown several strains to cause significant weight losses (i.e. ca 20%) in the temperate and tropical wood species, aspen (Populus tremula) and rubber wood (Hevea brasiliensis). In addition to the consumption of soluble carbohydrates and extractives, major changes in the ultrastructure of fibre cell walls was apparent with rapid attack of the gelatinous layer noted. In both wood species following G layer degradation, early wood fibres showed true cell wall degradation with pronounced erosion attack suggesting that prior destruction of the G layer afforded greater accessibility and ease of attack of the outer secondary cell layers.
O Encinas, G F Daniel


EELS (Electron Energy Loss Spectroscopy) - a technique for quantification of nitrogen and other light elements in the cell wall
1999 - IRG/WP 99-20163
A literature survey was performed to find progress in techniques for monitoring penetration of synthetic resins in wood cell walls. Electron energy loss spectroscopy (EELS) in combination with transmission electron microscopy (TEM) was successfully applied for the high resolution examination of the distribution of a partly methylated hydroxymethyl melamine resin in Norway spruce (Picea abies Karst.) earlywood cell walls. The nitrogen of the resin was found as clearly detectable signals in all layers of the lignified cell wall, thus allowing the quantification of resin which had penetrated into the different layers.
A O Rapp, H Bestgen, W Adam, R-D Peek


Evidence for wood cell wall degradation by the blue stain fungus Botryodiplodia theobromae Pat
1994 - IRG/WP 94-10077
Botryodiplodia theobromae Pat., a world wide ubiquitous polyfagus sapstain fungus, was found able to destroy the cell walls of birch fibres (Betula verrucosa Ehrh.) but not Caribbean (Pinus caribaea var. hondurensis Barr. and Golf.) and Scots pine (Pinus sylvestris L.) tracheids. The fungus caused characteristic erosion of fibre cell walls similar to soft rot type 2; destruction of the S1 - S2 interface and delamination and degradation of the S2 layer. No attack of middle lamellar regions or birch vessel walls was noted.
O Encinas, G F Daniel


Étude in vitro de la colonisation et de la dégradation structurale du bois d'aubier de Pin sylvestre par la Mérule: Serpula lacrymans Schum. ex Fr. S. F. Gray
1979 - IRG/WP 198
The degradation of Scots pine sapwood cell walls by Serpula lacrymans, a brown rot fungus, is observed after various periods of exposure from two weeks to twelve weeks. The observation by microscopy shows that the hyphae of Serpula rapidly invade the wood tissues as cell wall degradation starts. That deterioration is not gradual, it is observed to be very irregular as well within the whole of the tissues as within one single tracheid considered alone. The enzymatic action occurs at a distance from the secreting hyphae, causing an irregular desintegration of the various layers of the wall. The degradation of the wall is observed and analysed by scanning electron microscopy.
D Dirol


Formation of soft rot cavities in relation to concentric layers in wood fibre walls
1983 - IRG/WP 1185
A large number of timber species attacked by soft rot have been examined using light microscopy. The S2 layers in a large number of the timbers exhibited special structural features in the form of thin concentric layers. Several observations indicate that these layers may be characterised as "weak" zones by being more easily degradable than the surrounding wall layers. The chemical structure of the concentric layers is not known although some suggestions regarding their composition are given. It was observed that soft rot cavities regularly formed in the thin concentric layers. A hypothesis is put forward suggesting that T-branching occurs as a response to a chemical stimulus, possibly by sugars released by penetrating hyphae when they transverse the thin concentric layers.
T Nilsson, G F Daniel


Changes in pore structure and cell wall volume in wood decayed by brown- and white-rot fungi
1991 - IRG/WP 1501
Sweetgum (Liquidambar styraciflua L.) wood blocks were decayed by Postia (=Poria) placenta or Phanerochaete chrysosporium in soil-block cultures. Decay was terminated at various weight losses, and the pore volumes available to probes of various molecular weight and diameter were determined by the solute exclusion technique (Stone, J.E. and A.M. Scallan. 1968. Cellulose Chem. Technol. 2, 343-358.). The volume in sound (undecayed) wood that was accessible to the probes varied from 1.0 ml g-1 for the largest to 1.35 ml g-1 for water. Thus, the volume in sound wood attributable to cell wall was 0.35 ml g-1. In brown-rotted samples, the volume of pores in the cell wall increased steadily to 0.7 ml g-1at 35% weight loss. New cell wall volume was accessible to low molecular weight probes but not to molecules of Mr ³ 6,000. Within experimental error, no pores of > 20Å were observed in sound wood or >38Å in brown-rotted wood. Most of the new cell wall volume create by rermoval of components during decay was in the pore size range of 12Å to 38Å. Our results are consistent with the hypothesis that the initial depolymerization of cellulose, characteristic of brown rot, is caused by a diffusible agent. The molecular diameter of the agent is apparently in the range 12Å to 38Å and it causes erosion and thus enlargement of the pores to which it has access. In the white-rotted wood, cell wall volume increased to 0.6 ml g-1 at 40% weight loss and maximum pore diameter increased to 50Å. Most of the cell wall volume increase resulted from the creation of pore of 20-50Å diameter. Analysis of loss of major wood components as a function of weight loss revealed that lignin, cellulose, and hemicellulose were removed at approximately equal rates. Under our experimental conditions, ligninolytic enzymes have access to only a small portion of the new cell wall volume, even after extensive decay.
D S Flournoy


Soft rot decay of Belian (Eusideroxylon zwageri) wood
1995 - IRG/WP 95-10119
The heartwood of Belian (Eusideroxylon zwageri), an East Malaysian timber species, is naturally durable due to its certain unique anatomical features and high content of extractives. The timber can tolerate years of exposure to hazardous conditions in ground contact and other situations without any significant loss in its strength. A few Belian transmission poles sampled from one locality in Sarawak showed only surface heartwood decay at the groundline after 20 years. Transmission electron microscopy (TEM) revealed the presence of soft rot type cavities in fibre walls. In addition to soft rot attack of secondary walls, in severely decayed tissues, other areas of fibre walls, including the highly lignified middle lamellae, were also degraded. Bacteria were also abundant in these cells, suggesting that disintegration of wood tissues at the surface could result from a combined action of soft rot fungi and wood degrading bacteria.
A H H Wong, A P Singh


Microbial decay of an archaeological wood
1994 - IRG/WP 94-10053
A light and transmission electron microscopic investigation of an archaeological wood was undertaken to determine the cause of its deterioration. The wood came from a bulwark constructed in early 1100 in the lake Tingstäde Träsk on the island Gotland in Sweden. The samples of the wood, which was identified as Pinus sylvestris, were taken from a depth of 0.85 m below the bottom level. The wood was found to be heavily deteriorated, and from the micromorphology of decay observed under light and transmission electron microscopes it was concluded that the wood had been largely attacked by erosion bacteria. The degradation of wood components was quite variable, some cell structures/types showing greater resistance than others. The S2 wall layer of axial tracheids, which formed the bulk of the wood, was degraded most. In comparison, ray tracheids appeared completely resistant. Other cell structures/types, such as pit borders of axial tracheids and ray parenchyma cells, displayed features that were intermediate between the extremes noted above. These features are discussed in the light of available information on bacterial erosion of wood cell walls and on chemical composition of these cell structures/types in pine wood.
A P Singh, T Nilsson, G F Daniel


Effect of microfibril orientation of bamboo cell wall on soft rot penetration hyphae
1994 - IRG/WP 94-10087
The effect of microfibrillar orientation of bamboo (Phyllostachys virideglaucescence) cell wall on the development of soft rot (Chaetomium globosum) penetration hyphae was investigated. It was found that the soft rot penetration hyphae normally followed the microfibril angle of the cell wall. Bamboo cell walls have alternating broad and narrow lamellae with different microfibrillar angles. The microfibrillar angle of the broad lamellae is mostly oriented vertically, whilst the narrow lamellae are mostly oriented horizontally. Soft rot penetration hyphae normally follow these microfibrillar angles.
O Sulaiman, R J Murphy


Degradation features of waterlogged archaeological compression wood
1998 - IRG/WP 98-10258
The degradation characteristics of waterlogged archaeological compression wood excavated in South Korea were examined by transmission electron microscopy (TEM) and confocal laser scanning microscopy (CLSM). Degradation of Pinus compression wood occurred mainly in the inner part of S2 layer. In contrast, the outer part of S2 layer remained relatively intact. CLSM and TEM showed the erosion type of bacterial attack to be dominant in the secondary cell walls of both severe and mild compression wood. However, in some cases middle lamella was also degraded, which suggests that other forms of microbial attacks, such as bacterial tunnelling, were also present. Bacterial erosion in the severe compression wood was mainly confined to the inner part of S2 layer whereas in the mild compression wood it also extended into outer part of S2 and the S1 layer. The extent of erosion correlated to the differences in the amount and distribution of lignin, particularly in the outer S2 layer between the severe and mild compression wood cells. These features are compared with the degradation of normal Pinus wood.
Yoon Soo Kim, A P Singh


Soft rot
1978 - IRG/WP 179
Soft rot decay of treated wood is examined with special reference to hardwoods treated with CCA. Factors which adversely affect the chances of protection of hardwoods against soft rot are discussed. The ratio of the volume of the fibre cell wall to the volume of the fibre lumen is presented as a major factor influencing final preservative concentration in the fibre cell wall, the major strength contributing unit in wood. It is proposed that hardwoods are not necessarily more susceptible to soft rot than are conifers and that 0.2% Cu.wt/wt on gross wood will give control of soft rot in permeable hardwoods. Present and potential soft rot problems of treated conifers in North America are examined.
C R Levy


Diffuse cavity formation in soft rot of pine
1992 - IRG/WP 92-1541
A new type of soft rot of southern pine longitudinal tracheids is described. In this type, soft rot cavities form by diffuse degradation of the S2 cell wall layer by hyphae growing within the cell wall. Erosion is diffuse and irregular as opposed to the restricted, periodic erosion typical of type 1 soft rot cavity formation. Proboscis hyphae remain small (diameter 0.6 to 0.8 µm) and rapidly autolyze. These proboscis hyphae are not easily recognizable with light microscopy, especially at later decay stages, and require transmission electron microscopy to confirm their presence. This may be an alternative interpretation of the type 2 soft rot of softwoods described previously as being caused by lumenal hyphae through an intact S3.
S E Anagnost, J J Worrall, C J K Wang


Immuno-electron microscopic localization of extracellular metabolites in spruce wood decayed by brown-rot fungus Postia placenta
1990 - IRG/WP 1441
Degradation by Postia placenta in spruce and birch wood was shown to occur not only in the wood cell wall but also in the middle lamellae region. Middle lamellae was often found to be degraded along the centerline so that cells could separate along this line. Extracellular membrane structures were found surrounding the hyphae and this matrix labelled positively with antisera produced to Postia placenta extracellular metabolites. This matrix was also visible in the secondary wall of degraded birch wood. Antisera labelling was also noted in the secondary cell walls of the wood cells, but not in the middle lamellae region.
Y S Kim, B Goodell, J Jellison


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