Wood decomposition, higher fungi, and their role in nutrient redistribution

Abstract

Dead wood litter input to mature forest ecosystems represents 30–40% of 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 slowly, it represents a much larger proportion of the standing crop of plant 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 lesser extent ascomycetes. Readily available nutrients are utilized rapidly leaving other nutrients locked up in the recalcitrant lignocellulose 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 mycelial biomass. Formerly it was thought that nutrients were released when the carbon/nutrient ratio of the wood approximated that of mycelium. However, fungi are inherently greedy using excess nutrients for production of reproductive structures and foraging mycelium. The latter, which is often aggregated to form rhizomorphs or cords, grows out of wood in search of new resources, often forming extensive long-lived networks that exhibit remarkable patterns of reallocation of fungal biomass and nutrients. Within these systems, nutrients are conserved and are often relocated for many metres and may aid in establishment of mycelia in new resources. Nutrients are probably largely released when mycelia are grazed upon by invertebrates, nonbiotically damaged, interact with other fungi and bacteria, or die. Key words: ecology, lignocellulose, basidiomycetes, rhizomorph, translocation.