6 Wood Discoloration

54 3 Physiology
wounding a tree. A parasite may remain active as a saprobe for some 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 (Table 3.2), wood-inhabiting microorganisms
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 additionally
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 (Table
4.3). 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 (Chap. 9.5), molds, blue-stain fungi, red-streaking fungi in the
early stage (Chap. 6)] 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
sapwood parenchyma cells. 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 (Chap. 7) use
carbon additionally from the macromolecular cell wall components cellulose,
hemicelluloses and lignin (the latter only with the white-rot fungi) (Chap. 4).
Wood-inhabiting bacteria (Chap. 5.2) consume sugars and peptides of the
parenchyma cells and affect non-lignified cell tissue (parenchyma cells, epithelial
cells of the resin channels, sapwood bordered pits). Under natural
Table 3.2. Grouping of wood microorganisms according to nourishment and damages
wood inhabitants:
bacteria, slime fungi, yeasts,
staining fungi (molds, blue-stain fungi, red-streaking fungi at an early stage):
growth on the surface and/or in the outer wood area,
nutrition from the contents of parenchyma cells and sawwood capillary liquid
wood decayers:
brown-rot, white-rot, soft-rot fungi:
wood rot as a result of nourishment from the polymeric components
(cellulose, hemicelluloses, lignin) of the lignified cell wall
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