WOOD DECOMPOSITION, HIGHER FUNGI, AND THEIR ROLE IN NUTRIENT REDISTRIBUTION

Dead wood litter input to mature forest ecosystems represents 30-40% o f the total biomass, containing about 1-4 and 0.1-0.8 kg/(ha . year), of N and P, respectively. However, since wood decomposes relatively sl owly, it represents a much larger proportion of the standing crop of p lant litter on the forest floor, forming a large reservoir of mineral nutrients, which are unavailable for primary producers until they are released by decomposer organisms, primarily basidiomycetes and to a le sser extent ascomycetes. Readily available nutrients are utilized rapi dly leaving other nutrients locked up in the recalcitrant lignocellulo se complex. As decomposition proceeds the relative concentration of N and P in wood increases (i.e., carbon/nutrient ratio decreases), as C is lost as CO2, but these nutrients are rapidly sequestered in mycelia l biomass. Formerly it was thought that nutrients were released when t he carbon/nutrient ratio of the wood approximated that of mycelium. Ho wever, fungi are inherently greedy using excess nutrients for producti on of reproductive structures and foraging mycelium. The latter, which is often aggregated to form rhizomorphs or cords, grows out of wood i n search of new resources, often forming extensive long-lived networks that exhibit remarkable patterns of reallocation of fungal biomass an d nutrients. Within these systems, nutrients are conserved and are oft en relocated for many metres