The wood-inhabiting fungi as well as their colonization and damaging of wood are influenced by various physical/chemical and biological influences .
Physical/chemical factors comprise nutrients, water, air, temperature, pH value, light, and the force of gravity. Biological influences arise because of reciprocal effects between different organisms as antagonism, synergism, and symbiosis (e.g., Rypaek 1966; Kaarik 1975; Rayner and Boddy 1988). When investigating the various factors, laboratory methods do not reflect the situa-tion under natural conditions. Often it is difficult to vary a parameter without affecting the others. The individual factors in nature do not work isolated, but strengthen or weaken themselves mutually.
Table 3.1. Influences on fungal activity
physical/chemical:
nutrients, water, air, temperature, pH-value, light, force of gravity biological: antagonism, synergism, symbiosis
Nutrients
Fungi consist of about 90% water and 10% dry matter (chemical composition: Bétticher 1974). This dry matter has to be synthesized in the course of each hyphal division so that nutrients must be assimilated. Regarding the source of carbon, wood fungi are heterotrophic by using carbon from organic material, which derives from the autotrophic trees. In view of the biochemical way of nutrition, wood fungi are hemorganotrophic.
These fungi use organic compounds as hydrogen suppliers to produce energy from organic substances. This energy production is created by reduction-oxidation reactions (Schlegel 1992).Wood fungi are either parasites, which affect living tree tissue, or saprobes, Which grow on dead wood. Both forms can be obligatoryor facultative, as a saprobe may become a weakness or wound parasite with weakening or wounding a tree. A parasite may remain active as a saprobe forsome time after tree cutting.
Schmiedeknecht (1991) differentiated five main groups of the heterotrophic way of life: parasites, nekrophytes, which affect living hosts either as weakness parasites or kill them by toxic effect, sarkophytes, which prepare freshly died tissue for saprobes, saprobes, and symbionts (also Rayner and Boddy 1988). In view of the use of wood nutrients , wood-inhabiting microor-ganisms use carbon only from enzymatically easily accessible and digestible substrates, like simply constructed sugars, peptides, or fats, or from the storage material starch in the parenchyma cells.
The wood decay fungi use carbon ad-ditionally from the complex, main components of the woody cell wall, cellulose, hemicelluloses, and lignin. The cell wall components can be degraded either directly within the wood cell wall or only as a pure component after isolation from the cell wall . In the laboratory, sugars such as glucose, maltose (in malt extract), and saccharose are suitable C-sources for most wood fungi. The wood-inhabiting fungi [yeasts (, molds, blue-stain fungi, red-streaking fungi in the early stage . and the wood-decay fungi during initial decay nourish predominantly of sugars and other components in the wood parenchyma cells.
The quantity of these primary metabolites is usually below 10% related to the wood dry weight, and these metabolites occur usually only in living or just died
For example, soluble nutrients in wood increased its susceptibility to soft-rot fungi and bacteria in ground contact (Terziew and Nilsson 1999). In Pinus contorta wood samples, triglycerides were consumed and mannose was the most depleted sugar by several blue-stain fungi (Fleet et al. 2001). The wood-degrading brown, white and soft-rot fungi use carbon additionally from the macromolecular cell wall components cellulose, hemicelluloses and lignin (the latter only with the white-rot fungi) . Wood-inhabiting bacteria consume sugars and peptides of the parenchyma cells and affect non-lignified cell tissue (parenchyma cells, ep-ithelial cells of the resin channels, sapwood bordered pits). Under natural
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