Biological Decomposition of Solid Wood

Decomposition of wood is an important part of the carbon cycle of nature. Decomposition is caused by fungi, insects, and marine borers that use the wood as food or shelter, or both. Lignin in wood provides a physical barrier to enzymatic decomposition of cellulose and hemicelluloses. This barrier is breached mechanically by insects and marine borers, biochemically by whiteand soft-rot fungi, and possibly by small nonenzyme catal y s t s i n t h e c a s e o f b r o w n r o t f u n g i . C e l l u l o s e is degraded by endoand exo-glucanases and β-glucosidases, hemicelluloses by endo-glycanases and glycosidases, lignin by nonspecific enzymes, and perhaps by nonenzymatic, oxidative agents. Rapid strength loss occurs with all decay fungi; but especially with brown-rot fungi. Strength loss due to insect attack is roughly proportional to the amount of wood removed. Fungal decomposition of wood can be prevented by keeping it below its fiber-saturation moisture content (approximately 27% of its dry weight) and by using the heartwood of naturally durable woods (species) or preservative-treated wood. Useful application of wood-decomposing fungi is limited currently to production of edible mushrooms. Potential applications include biological pulping, pretreatment for enzymatic conversion of wood to sugars, and waste treatment. Many aspects of wood biodecomposition have not been researched adequately.