The pine stems were cut from three different polluted environments – Ist trees degradation degree (weak pollution), IInd trees degradation degree (strong pollution) and IIIrd trees degradation degree (connected with very strong pollution). On the basis of obtained results it was stated that environmental pollution caused changes in late wood participation, as well as distribution of cellulose on the stem cross- and longitudinal section. It also changed cellulose content in bark from the butt-end section, which was about 26% regardless the degradation degree. The environmental pollution caused also an increase of viscometric average polymerization degree of cellulose in heartwood in relation to heartwood adjacent sapwood and sapwood from butt-end section. Regardless the degradation degree, cellulose polymerization degree in heartwood adjacent sapwood from the middle part of the stem was higher in comparison to sapwood and heartwood. Moreover, the environmental pollution caused the increase of viscometric average polymerization degree of cellulose in bark. The polymerization degree of cellulose in bark from the butt-end section of IIIrd degradation degree stems was 22% and 23% higher in comparison to the Ist and IInd degradation degree.

The main objective of this research was to investigate tropical wood sorptive properties. For selected tropical wood species (courbaril, ipe, light red meranti, merbau, tatajuba, and teak), the equilibrium moisture content was determined at 20 °C and 9, 30, 55, 70, and 97% relative humidity. The experimentally determined values were analysed using the Hailwood-Horrobin sorption model to compute the fibre saturation point and mono-and multi-layer sorption. There were significant differences in the sorption behaviour of different wood species. Generally, the fibre saturation point of tropical wood species is lower than in wood species from moderate climate zones. The lowest values of fibre saturation point were found for ipe (18.7%), courbaril (20.4%), and tatajuba (20.5%). Furthermore, chloroform-ethanol extractives content was correlated with multilayer sorption and the fibre saturation point, such that a higher content of chloroform-ethanol extractives was associated with a lower equilibrium moisture content. Therefore, chemisorption was not influenced by chloroform-ethanol extractives. Ethanol extracts showed an influence on monomolecular-bound water.

Black poplar (Populus nigra L.) was thermally modified in nitrogen atmosphere. The effects of the modification process on poplar wood were evaluated for temperatures: 160 °C, 190 °C, and 220 °C applied for 2 h; and 160 °C and 190 °C for 6 h. The percentual impact of temperature and time of modification on the properties of modified wood was analysed. The study permitted the identification correlations between the chemical composition and selected physical properties of thermally modified poplar wood. The dimensional stability of poplar wood was improved after thermal modification in nitrogen. The higher the temperature of modification, the lower the equilibrium moisture content (EMC) of black poplar. At the temperature of 220 °C, EMC was two times lower than the EMC of non-modified black poplar. It is also possible to reduce the dimensional changes of wood two-fold (at the modification temperature of 220 °C), both in radial and tangential directions, independently of the acclimatization conditions (from 34% to 98% relative humidity, RH). Similar correlations have been found for wood that has been soaked in water. Higher modification temperatures and longer processing times contributed to a lower swelling anisotropy (SA).

The phytoalexin deficient 4 (PAD4) gene in Arabidopsis thaliana (AtPAD4) is involved in the regulation of plant--pathogen interactions. The role of PAD4 in woody plants is not known; therefore, we characterized its function in hybrid aspen and its role in reactive oxygen species (ROS)-dependent signalling and wood development. Three independent transgenic lines with different suppression levels of poplar PAD expression were generated. All these lines displayed deregulated ROS metabolism, which was manifested by an increased H2O2 level in the leaves and shoots, and higher activities of manganese superoxide dismutase (MnSOD) and catalase (CAT) in the leaves in comparison to the wild-type plants. However, no changes in non-photochemical quenching (NPQ) between the transgenic lines and wild type were observed in the leaves. Moreover, changes in the ROS metabolism in the pad4 transgenic lines positively correlated with wood formation. A higher rate of cell division, decreased tracheid average size and numbers, and increased cell wall thickness were observed. The results presented here suggest that the Populus tremula × tremuloides PAD gene might be involved in the regulation of cellular ROS homeostasis and in the cell division--cell death balance that is associated with wood development.

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