Brown-rot fungi, which grow mainly on softwoods, represent
only 7% of wood-rotting basidiomycetes. This group of basidiomycetes
can degrade wood polysaccharides after only a partial
modification of lignin, resulting in a brown material consisting of
oxidized lignin, which represents a potential source of aromatic
compounds for the stable organic matter fraction in forest soils.
Although only white-rot and brown-rot basidiomycetes
can degrade wood extensively, some ascomycetes and their
asexual states, the so-called deuteromycetes, can colonize
wood in contact with soil. This results in a decrease in the
mechanical properties of wood, giving rise to so-called softrot,
a process that often involves bacteria (Table 1). Soft-rot
fungi can degrade wood under extreme environmental conditions
(high or low water potential) that prohibit the activity of
other fungi. Moreover, some basidiomycetes also cause a softrot-
type decay pattern. Finally, a limited number of ascomycetous
fungi, called stain fungi, can colonize wood through
parenchymatic rays and resin channels causing discoloration of
softwood tissues but a very limited degradation, which mainly
affects extractives and water-soluble materials.