Microclimatic conditions, notably water content and temperature (Boddy, 1984, 1986), are major determinants of fungal community development in wood (see reviews in Rayner and Boddy, 1988; Boddy, 2001). Low water availability impedes metabolic functioning, while high water contents impose poor aeration and hence restrict aerobic processes, including fungal wood decay. Both extremes typically result in mycelial death if prolonged (Chapter 4). Similarly, low temperatures decrease the rate of metabolic activity, while high temperatures are detrimental to enzyme function, and can result in death (Chapter 4). Temperature and water regime also affect the balance in combative interactions (Boddy, 2000; Chapter 7).

Some wood-inhabiting fungi have evolved to cope with some of these extremes and predominate under appropriate conditions, i.e. they are S-selected. For example, the mycelium of many pyrenomycetes is tolerant of very dry conditions (Boddy et al., 1985,1989), whereas the mycelium of Basidiomycota tends not to be, though some are desiccation tolerant by virtue of resting spores, e.g. H. paradoxa produces chlamydospres, with rapid resumption of mycelial growth when conditions improve. Some polypores associated with sun-exposed logs are able to resist very high temperatures, e.g. Gloeophyllum abietinum, G. sepiarium and G. trabeum 4 h at 95 °C (Huckfeldt et al., 2005). The majority of Basidiomycota can probably survive freezing, and some certainly remain active at temperatures approaching freezing, several corticoid basidiomycetes producing actively sporu-lating sporocarps under snow (Gilbertson, 1973); the agarics Pleurotus ostreatus and Flammulina velutipes produce sporocarps resistant to subzero temperatures, reinitiating active growth during milder periods (Yakovlev et al., 2000).

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