The hygroscopicity and thermodynamic properties of juvenile Pinus sylvestris L. wood taken from the submerged piles of a bridge built in 1903 over the Jiloca River, in Spain, were compared with the corresponding values of juvenile wood of the same species from recently cut trees. The 35°C and 50°C isotherms were plotted and subsequently fitted using the Guggenheim-Anderson-Boer-Dent method, and the isosteric heat of sorption was obtained through the integration method of the Clausius-Clapeyron equation. The isotherms were compared by means of the hysteresis coefficients. Infrared spectra were recorded to study the chemical modifications, and the crystal structure of the cellulose was studied by X-ray diffractograms. The submersion in water resulted in hemicellulose degradation and a decrease in the crystallinity index and the crystallite length, accompanied by a corresponding increase in the proportion of amorphous zones. Owing to this, the equilibrium moisture contents of the water logged wood are higher than in the recent wood, both in adsorption and in desorption. In terms of the thermodynamic properties, the bond energy is higher in the recent wood than in the water logged wood.

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The main objective of this study was to identify differential anatomical features between Ulmus pumila L. and Ulmus minor Mill. clones resistant to Dutch elm disease and U. minor clones susceptible to Dutch elm disease, with a focus on the intervascular pits and medullary rays. Resistant elms showed lower mean values than susceptible elms for pit membrane diameter, pit aperture area, pit membrane abundance per vessel-wall area, ray width, and ray tangential area. A principal component analysis of the parameters measured revealed slight differentiation between species but clearly grouped U. minor clones according to their susceptibility group. In comparison with susceptible elms, the pit structure observed in resistant elms may limit passive fungal spread within the sapflow, lower the probability of fungal cells passively reaching pit membranes, and reduce the vulnerability of the xylem to cavitation. Similarly, the ray structure observed in the resistant elms is likely to reduce the amount of easily accessible nutrients available for fungal growth as well as the rate of radial colonization in comparison with susceptible elms. Examination of the principal component loadings suggested that susceptible U. minor clones were mainly characterized by enhanced values of pit membrane abundance per vessel-wall area relative to resistant U. minor trees.Résumé : L'objectif principal de cette étude était d'identifier les différences dans les caractéristiques anatomiques entre des clones d'Ulmus pumila L. et d'U. minor Mill. résistants à la maladie hollandaise de l'orme et des clones d'U. minor sensibles à la maladie hollandaise de l'orme en mettant l'accent sur les ponctuations intervasculaires et les rayons médul-laires. Le diamètre des membranes de ponctuations, la superficie de l'ouverture des ponctuations et l'abondance des membranes de ponctuations par unité de surface des parois des vaisseaux, de largeur des rayons et de superficie tangentielle des rayons étaient en moyenne plus faibles chez les ormes résistants. Une analyse en composantes principales des paramètres qui ont été mesurés a révélé une légère différentiation entre les espèces mais a clairement regroupé les clones d'U. minor selon leur groupe de sensibilité. Comparativement aux ormes sensibles, la structure des ponctuations observée chez les ormes résistants pourrait limiter la propagation passive du champignon avec le mouvement de la sève, réduire la probabilité que les cellules fongiques atteignent passivement les membranes de ponctuations et diminuer la vulnérabilité du xylème à la cavitation. De la même façon, la structure des rayons observée chez les ormes résistants réduit probablement la quantité de nutriments facilement accessibles et disponibles pour la croissance du champignon ainsi que le taux de colonisation radiale comparativement aux ormes sensibles. L'examen de la saturation des composantes principales indique que les clones sensibles d'U. minor étaient principalement caractérisés par des valeurs plus élevées de l'abondance des membranes de po...

The Spanish populations of Pinus sylvestris L. occupy differentiated sites and must therefore include structural variations to cope with varied climate conditions. This study compares wood anatomical traits of P. sylvestris from ten Spanish regions of provenance with contrasting climates, taking into account the effects of region of provenance and tree nested within provenance on variation in wood biometry. In general, the effect of both sources of variation (provenance and tree) on wood biometry was highly significant. Most of the anatomical variations observed were intra-populational (at the tree level), although variation explained by provenance was high for some parameters (e.g., ray frequency and ray parenchyma cell frequency), suggesting high environmental influence. Trees in the driest region, growing in a Mediterranean phytoclimate, were characterized by large tracheid lumens, suggesting more efficient water conduction. They also had thick cell walls, which would reduce the risk of cavitation caused by high implosion stress during periods of drought, as well as a high ray tracheid frequency, implying greater water storage capacity in the sapwood. The population with greatest growth, located in an oroboreal phytoclimate, was characterized by large bordered pits and long tracheids, which would reduce resistivity in water transport. At higher altitudes, tracheid lumen diameter and resin canal diameter tended to be smaller, and intertracheid wall strength was greater. Results are discussed in relation to adaptation of the species to growth demands and frost.