Archaeological wood of 13 excavated oak piles from five historical bridge generations in Bavaria, dated from 1447 to 1787, was investigated by means of light microscopy (LM) and cellular ...UV-microspectrophotometry (UMSP) to study the ageing and natural resistance of the excavated wood. Furthermore, the mineral content of the ancient wood was determined to evaluate the impact of mineral inclusions on microbial resistance, tested using a mini block fungal test. The LM and UMSP analyses revealed well preserved cell wall structures and no significant modification of the lignin composition and distribution in predominant parts of the piles. Slight microbial decay caused by soft rot and erosion bacteria was only detectable at the outermost millimetres of individual piles. The fungal mini block tests yielded mass losses of ancient oak samples between 15% and 30%, independent of their analysed mineral content. The results provided evidence that the fungal resistance of the investigated ancient wood is mainly determined from the special soil with its high mineral content.
The colour of Sapelli heartwood (Entandrophragma cylindricum Sprague) is variable depending on habitat. In recent years an unusual pinkish-brown colour has been observed in commercial sawn timber of ...this species from Central Africa. Initial studies of Sapelli heartwood samples from various provenances have furthermore demonstrated pronounced differences in its decay resistance. Heartwood extractive composition varies considerably between provenances. Samples of Sapelli heartwood from the Central African Republic (RCA) contained 6.4% by weight of extractives compared with 12.5% for those from Cameroon and four other provenances investigated. UV microspectrophotometric analysis of heartwood extractives was used to localise phenolic extractives within wood cell walls and to identify their distribution at tissue level. The S2 and S3 wall layers of vessels and fibres in the heartwood were discriminated from sapwood by their high concentration of non-lignin phenolic extractives. These extractives in the cell walls were also found to be variable. As UV absorption properties show, the vessel and fibre secondary walls of Cameroon heartwood had a considerably higher concentration of extractives in comparison with samples from the RCA. In sapwood, the UV absorption levels for the fibre S2 layer and the vessel S3 layer were independent of the extraction procedure, suggesting the phenolic extractives in this part of the trunk were in low concentrations. Furthermore it is suggested that polyphenols constitute part of the cell wall matrix. The non-extractable phenolic content was found to be independent of provenances as demonstrated by wood from Cameroon and the RCA. The natural durability of Sapelli heartwood against fungal decay appears to be dependent on the extractive composition and on their concentration in the fibre tissue.
Investigations on the manufacture of the oak panels and the dendrochronological dating of the wood of two paintings titled "The Incredulity of Thomas" serve as an aid to the art historian to verify ...the relationship between these two versions. It turned out that the painting "The Incredulity of Thomas" (private property, Chicago) is more or less contemporary with the version signed Rembrandt f. 1634 (Pushkin State Museum of Fine Art, Moscow). Moreover, the dendrochronological dating identified the wood of the panel of the Chicago painting as comingfrom the same oak tree as that used for the panel of the painting titled "A man in oriental costume" signed Rembrandt f. 1633. This indicates that the same "Schilder maker" workshop had supplied the Rembrandt atelier also with a specifically ordered panel for the Chicago painting, nearly identical in size and quality as the panel of the painting Bred. 552.
The width of the increment zones in the xylem of Swietenia macrophylla King and Cedrela odorata L. was investigated by dendroecological methods in a primary forest near Aripuanã, Mato Grosso, Brazil ...(10°09'S, 59°26'W). The annual period of cambial cell division and its intra-annual variation were determined by dendrometer measurements of 30 trees of each species. Tree-ring width chronologies for Swietenia and Cedrela were developed from cross-dated increment curves of 33 out of 47 Swietenia and 51 out of 64 Cedrela trees. Simple correlations were computed between the radial growth increment and monthly precipitation for the period 1890-2000. In Swietenia, cambium activity occurred throughout almost the whole year, but in Cedrela it was restricted to the rainy period from September of the previous year to June of the current year. Tree-rings were formed annually in the juvenile and adult wood of Cedrela, while in Swietenia the annual formation of tree-rings was restricted to the adult wood. Consequently the age of the Swietenia trees could be dated by the tree-rings in good approximation, while age dating of the Cedrela trees was exact. Correlation analyses revealed a significant relationship between the precipitation at the beginning and at the end of the growth season and the width of the increment zones in the adult xylem of Swietenia. In contrast, the width of the growth increment in the xylem of Cedrela was significantly correlated with the precipitation in March and May of the previous growth period.PUBLICATION ABSTRACT
The biological, chemical and technological study of waterlogged archaeological piles of oak wood (
Quercus petraea
(Matt.)Liebl.) of a medieval bridge in Bavaria was primarily undertaken in the ...context of finding an adequate drying method to assure stable long-term conditions while presenting the archaeological finds in a local history museum. There was a unique chance to study the oak wood preservation of five generations of a bridge foundation from one and the same place. According to the dendrochronological dating of the felling dates of the oaks, the first identified generation is already medieval with an earliest date of 1447, followed by the second generation at about 1572, with the third one at about 1658, the fourth one at about 1727 and the youngest one at about 1787. The experienced selection of the trees in the forest and the subsequent careful manufacture of the piles without any sapwood and obviously their immediate application allowed for studying the alteration of the wood characteristics with increasing years of underground pile exposure. The light microscopical study did not reveal remarkable structural alterations of lignin and cellulose. Microbial activities of erosion bacteria and soft rot could only be detected within the uppermost rounded part of some piles and in their periphery. However, it was informative to see how green and wet manufactured oak wood responds as a sensitive ion-exchange system underground. The iron ions penetrated particularly into the outer heartwood and reacted with the special accessory compounds, such as tannins, essentially within the parenchyma cells. However, the radial distinct gradient had no notable difference between the fifth generation (1787) and the older ones. The uptake of Si-, Ca- and Mg-ions significantly represents an influx with a radial penetration even to the pith. Surprisingly, the monomeric K-ions, which are present in the green woody tissue with a mean value of 330 ppm moved radially out of the wood, down to about 10% compared to the beginning of the underground exposure. Moreover, the shift of the original pH value of about 3.6 of the heartwood to finally a mean of pH 4.6 clearly underlines a correlated efflux effect, which might slightly chemically alter the woody tissue. The changes of the chemical and technological characteristics such as basic density, compression strength, sorption behavior, shrinkage, and ash content actually indicate that over the centuries some change in the chemical characteristics of the heartwood must have occurred.
The topochemical distribution of phenolic extractives in steamed and kiln-dried beechwood with discolourations was investigated on a cellular level by using scanning UV microspectrophotometry (UMSP). ...For the chemical characterisation of accessory compounds, acetone and methanol extracts of the discoloured beechwood were separated by accelerated solvent extraction (ASE) and analysed with high performance liquid chromatography (HPLC). The UV microscopic investigations reveal that the accessory compounds responsible for the discolouration of beechwood are mainly restricted to the longitudinal and ray parenchyma cells and the lumen of vessels. The detected extractives are characterised by high UV absorbance values and an absorbance maximum in a wavelength range between 280 and 290 nm. The separation of the acetone and methanol extracts of discoloured beechwood shows the presence of different low molecular phenols such as catechin and 2,6-dimethoxybenzochinon, which are transformed into high condensation compounds during steaming and kiln-drying.
The entry of calcium and magnesium from external sources into mycorrhizal roots of 3-year-old Norway spruce trees (Picea abies L. Karst.) was monitored. Roots of intact plants were exposed for ...various periods of time, ranging from 2 min to 48 h, to nutrient solutions which contained the stable-isotope tracers 25Mg and 44Ca. After labelling, samples of roots were excised from the plants, shock-frozen, cryosubstituted and embedded. The resulting isotope composition in this material was analysed by a laser-microprobe-mass-analyser (LAMMA) at relevant positions within cross-sections of the roots. For both elements, we determined (i) the fractions of the isotopes originating from the plant prior to labelling, and (ii) the fraction of isotopes originating from the corresponding tracer that penetrated into the root. Both divalent cations rapidly penetrated across the cortical apoplast and reached the endodermis. After 2 min of exposure to the labelling solution, an initial transient gradient of the tracers could be observed within the root cortex. Subsequently, calcium as well as magnesium equilibrated between the apoplast of the entire cortex and the external tracer with a half-time, t1/2, of about 3 min. In contrast, the kinetics of radial movement into the vascular stele showed a delay with a t1/2 of 100—120 min. We take this as strong evidence that there exists a free apoplastic path for divalent cations in the cortex and that the endodermis is a major barrier to the further passage of Mg and Ca into the xylem. While 25Mg in the labelling solution exchanged rapidly with Mg in the cortical apoplast, the exchange across the plasma membrane with Mg present in the protoplasm of the same cortical cells was almost 2 orders of magnitude slower. The kinetics of Ca and Mg entry at +6 °C were similar to those obtained at a root temperature of +22 °C.
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