Air

      As aerobic organisms, wood fungi produce CO2, water, and energy by respira-tion and need therefore air oxygen . 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 02 and high CO2 content, respectively. The 02 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 x 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 oxy-gen, such as degradation of lignin, oxidative polymerization of phenols, and melanin synthesis in blue-stain fungi and other fungi. With the onset of differ-entiation, 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 sen-sitively to 09 lack than parasites living within the heartwood: The saprobes 

Table 3.3. Aerobic degradation of wood to CO2, water and energy 

cellulose, hemicellulose, lignin from wood - (ectoenzymes) ---4- sugars, lignin derivates - (uptake, intracellular enzymes) 
CO2 + 2(H) 2(H) + 1/202 - (respiratory chain) —> H2O + energy (ATP) 


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 x 162 = 486, 486 g cellulose yield 8,505 kJ (2,025 kcal) 

 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 sen-sitively to 02 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% 02 content compared to 200/6 (Lindberg 1992). The conidia of some blue-stain fungi still germinated at 0.25% 02 content, some Mucoraceae (molds) even in a pure N-atmosphere (Reif; 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 trans-ferred 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). In the course of wood degradation, the CO2 concentration may increase. Some wood-degrading Basidiomycetes, particularly heartwood destroyer, are tolerant of a high CO) content, since they grew well at 70% C.02 and ev.en. at 100% (Hintikka 1982), while forest-litter decomposing fungi were inhibited