The effect of thermo-hydro treatment (THT) on the properties of birch (Betula spp.) wood veneers has been studied. THT was carried out in a multi-functional pilot scale wood modification device of wood treatment technology (WTT, Latvia) under elevated water vapor pressure conditions at four combinations of temperature and treatment time (°C/min): 150/10; 150/50; 160/10 and 160/50. After THT, the following veneer properties were examined: mass loss (ML), chemical composition, bending strength (BS), tensile strength (TS), equilibrium moisture content (EMC), resistance to decay by mould and blue stain fungi, and surface contact angle (CA). The chemical components were changed by THT. Increased THT temperature and time resulted in hydrophobization of veneers as indicated by decreasing EMC and increasing CA data. All THT were effective against wood discoloring fungi, although insufficient decay resistance was observed. The mechanical strength properties of THT veneers were also deteriorated.
Wood plastic composites (WPC) are mainly used as an outdoor material, so durability against fungal decay is one of the factors that should be analyzed and if necessary improved. WPC are susceptible to biodegradation, although these materials have limited water absorption because of the wood fiber encapsulation in polymer matrix. In the study two different water pretreatment methods (short-term and long-term) were used to ensure appropriate water content for fungal growth. Also in the paper thermally modified wood (different regimes) fiber influence on WPC fungal resistance is investigated. The results showed that long-term water pretreated WPC specimens had more suitable conditions for fungal degradation that led to higher weight loss. The results which were related to thermally modified wood fibers showed, that WPC with thermally modified wood fibers had improved resistance against fungi. Thermal modification regimes had an effect on WPC durability as well.
Soil microbial populations in the Northern Temperate Zone have been poorly studied in comparison with extreme environments. The aim of the work was to study the seasonal changes in the microbial populations of spruce forest soil of the Northern Temperate Zone using classical methods of microbiology and molecular biology. Upper horizons in two Picea abies stands on sodpodzolic and illuvial humus podzol soil were analysed. Sampling was done monthly over a period of twelve months (May 2009-April 2010). Microbial communities in both experimental plots showed different responses to the analysed environmental factors. In the sod-podzolic soil only the fungal DNA amount was significantly higher in the rest period (October-April) in comparison with the active vegetation period (May-September) and the number of Pénicillium spp. colonies was larger in the active vegetation period. In the other soil the number of maltose utilizing bacteria, yeasts, and Pénicillium spp. and other culturable filamentous fungi was significantly higher in the active vegetation period, while the fungal DNA amount was elevated in the rest period. Although ARDRA did not reveal differences, sequencing of 84 fungal isolates showed different compositions of the communities. Sorensen's index between the plots was low (0.29). Comparing the active vegetation period with the rest period, the index was higher (0.48). Although all tested fungal isolates from the rest period were able to grow at 4°C, none of them showed psychrotrophic growth characters.
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