| Summary: | Translocation of nitrogen (N) through mycelial cords of wood decay fungi is thought to be the mechanism responsible for the observed increase in absolute N content in woody debris over time. This research evaluates the ability of the mycelial cords of the wood ¹⁵decay fungus Hypholoma fasciculare to translocate and accumulate labeled organic (¹⁵N-glycine, N Douglas-fir litter) and inorganic N (¹⁵NH₄⁺, ¹⁵NO₃⁻) in its wood substrate. Each N form was supplied separately to the growing fronts of mycelial cords established over 67 days from wood blocks (Douglas-fir) in soil microcosms. Three sampling occasions (days 6, 18 and 30 after N addition) were used to identify trends in ¹⁵N transfer and total N accumulation. Wood blocks inoculated with Hypholoma fasciculare assimilated significantly more ¹⁵N than uninoculated blocks for all ¹⁵N treatments on at least one sampling occasion. After 73 days of incubation (day 6 sampling occasion), inoculated wood blocks increased in absolute N content by 211% relative to uninoculated control blocks, but 80% of this accumulated N was lost after 97 days of incubation (day 30 sampling occasion). The small amount of ¹⁵N that was transferred contrasted with the large increase in total N, suggesting that the site of N transfer was largely from the soil underneath wood blocks rather than at the site of ¹⁵N injection. The precipitous decline in absolute N content was attributed to visible indications of mycelial senescence. This research demonstrates that the mycelial cords of Hypoloma fasciculare are capable of translocating ¹⁵N into a wood substrate and can also greatly increase the absolute N content of wood blocks. The results are discussed in the context of fungal ecology as well as woody debris management.
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