Nitrogen isotopes, carbon isotopes, and pyrolysis products in wood decay fungi, woody tissues, and cellulose from a long-term log decomposition experiment at H.J. Andrews Experimental Forest, Oregon, USA

We combined elemental, isotopic, and compositional patterns in wood, cellulose, and sporocarps to investigate functional and isotopic differences in six taxa of decay fungi during log decomposition. Fungal protein was 4-5‰ higher in δ15N and 3-4‰ higher in δ13C than non-protein. Fungal δ15N correlated with the proportion of protein in N-containing pyrolysis products. 15N partitioning between protein and non-protein pools in mycelia prior to sporocarp formation controlled sporocarp δ15N relative to N sources. Radiocarbon measurements separated fungi into heartwood colonizers (Fomitopsis and Hericium, ~30+-year-old carbon) and sapwood colonizers (Mycena, Hypholoma, and Trametes, 1-12-year-old carbon). Sporocarps were 0-2.5‰ higher in δ13C than wood cellulose; this was attributed to compositional differences, assimilation of some 13C-enriched hemicellulose or sucrose, and 13C discrimination during metabolism. Research highlights included: (1) Strategies of carbon and nitrogen acquisition differ among wood decay fungi, (2) Fungal taxa varied widely in chemical composition as assessed by pyrolysis GC-MS, (3) Fungal carbon was from one (Mycena) to 30+ years (Fomitopsis, Hericium) old, (4) Hericium preferentially assimilated 13C-enriched hemicellulose, (5) The removal of 13C-depleted C6 atoms in pentoses causes high 13C in hemicellulose, (6) taxa varied in N partitioning among sporocarps, mycelia, protein, and non-protein. From these measurements, we improved the quantitative and conceptual understanding of how sources, composition and metabolic processing determined isotopic composition of fungi.