6 Wood Discoloration

3.2 Air 59
Table 3.4. Energy production from wood cellulose
Assuming that 1 kg dry wood contains 48.6% cellulose:
1 mol glucose (180 g) yields 2,835 kJ,
180 g glucose correspond to 162 g cellulose
[162 + 18; (1 mol H2O used for hydrolysis)],
3 × 162 = 486,
486 g cellulose yield 8,505 kJ (2,025 kcal)
content in the wood of living oak trees varied season-dependently from 1–4%
and the CO2-content from 15–20% (Jensen 1969).
There are various reactions occurring in wood fungi that require oxygen,
such as degradation of lignin, oxidative polymerization of phenols, and
melanin synthesis in blue-stain fungi and other fungi. With the onset of differentiation,
there is also an increased oxygen demand. When the reproduction
is initiated, there is a high requirement for protein and nucleic acid synthesis,
which energetically involves a higher demand on the fungal metabolism and,
thus, increased oxygen utilization (Jennings and Lysek 1999). This reason as
well as access to air currents for spore dispersal explain why most fungi form
their fruit bodies at or near the substrate surface.
A lack of oxygen can limit wood decay. Saprobes usually react more sensitively
to O2 lack than parasites living within the heartwood: The saprobes
Serpula lacrymans and Coniophora puteana survived without oxygen 2 and
7 days, respectively (Bavendamm 1936), the parasitic heartwood destroyer
Laetiporus sulphureus more than 2 years (Scheffer 1986). In Heterobasidion
annosum, mycelial growth hardly decreased at 0.1% O2 content compared to
20% (Lindberg 1992). The conidia of some blue-stain fungi still germinated
at 0.25% O2 content, some Mucoraceae (molds) even in a pure N-atmosphere
(Reiß 1997).
The yeasts, which are able to get energy also facultatively anaerobically
by fermentation, form an exception of the aerobic way of life among the
fungi. During the alcoholic fermentation of the hexose sugars (Saddler and
Gregg 1998) in coniferous wood sulphite spent liquors which was performed
in former times e.g., in Switzerland, the produced hydrogen is not transferred
to atmospheric oxygen, but to the organic H-acceptor acetaldehyde:
2(H) + CH3CHO → CH3CH2OH (ethanol). At low oxygen content, anaerobic
metabolites like ethanol, methanol, acetic acid, lactic acid, and propionic acid
have been found also in Basidiomycetes (Hintikka 1982).
Inthecourseofwooddegradation,theCO2 concentration may increase.
Some wood-degrading Basidiomycetes, particularly heartwood destroyer, are
tolerant of a high CO2 content, since they grew well at 70% CO2 and even at
100% (Hintikka 1982), while forest-litter decomposing fungi were inhibited
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