6 Wood Discoloration

58 3 Physiology
durability of many heartwood species develop during heartwood formation
from starch and soluble carbohydrates (Magel 2000) and are mainly phenols,
like terpenoids, flavonoids, stilbenes, and tannins (Fengel and Wegener 1989;
Obst 1998; Roffael and Schäfer 1998; Imai et al. 2005). For example, pinosylvins
inhibited brown-rot fungi (Celimene et al. 1999), flavonoids inhibited Gloeophyllum
trabeum and Trametes versicolor (Reyes-Chilpa et al. 1998). While the
extractives during the obligatory formation of a colored heartwood penetrate
in the cell walls, those that develop by exogenous influences (facultatively colored
heartwood), like wound reactions, do not impregnate cell walls (Koch
2004).
Omnivors are the only less specialized molds (Chap. 6.1), which can grow on
wood, paper, wallpaper, books and leather, and dissolve even minerals from
glass by acid production (Kerner-Gang and Schneider 1969). The “polyphage”
H. annosum has a broad host spectrum of over 200 wood species (Heydeck
2000). As a specialized parasite, Piptoporus betulinus attacks only birch trees
(host spectrum: Jahn 1990; Ryvarden and Gilbertson 1993).
Nutrient media to isolate, enrich, purify, and cultivate wood-inhabiting
fungi are malt extract agar and potato dextrose agar of about pH 5.5. Bacterial
isolates from wood grow on nutrient media like peptone/meat extract/yeast
extract of about pH 7 (Schmidt and Liese 1994). For special microorganisms,
selective media are commercially available, or standard agar is enriched with
selecting compounds. If bacteria have to be eliminated during fungal isolations,
the substrate can be acidified by lactic or malic acid or an antibiotic is
added. Orthophenylphenol selects on white-rot fungi. Benomyl inhibits molds
like Penicillium and Trichoderma species.
3.2
Air
As aerobic organisms, wood fungi produce CO2, water, and energy by respiration
and need therefore air oxygen (Table 3.3).
The energy production from wood, if only cellulose is consumed, is shown
in Table 3.4. Aerobes, however, do not respire carbohydrates totally, but use
intermediates for their metabolism.
Fungal activity is affected by the composition of the gaseous phase. Usually
wood decay decreases at low O2 and high CO2 content, respectively. The O2
Table 3.3. Aerobic degradation of wood to CO2, water and energy
cellulose, hemicellulose, lignin from wood – (ectoenzymes) →
sugars, lignin derivates – (uptake, intracellular enzymes) → CO2 +2(H)
2(H) + 1/2O2 – (respiratory chain) → H2O + energy (ATP)
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