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.

本研究整合木材、纤维素与子实体（Sporocarp）的元素、同位素及组成特征，探究原木分解过程中6个类群腐朽真菌的功能与同位素差异。真菌蛋白的δ¹⁵N值较非蛋白组分高4‰~5‰，δ¹³C值较非蛋白组分高3‰~4‰。真菌的δ¹⁵N值与含氮热解产物中的蛋白占比呈显著相关。子实体形成前，菌丝体（Mycelium）中蛋白与非蛋白库之间的¹⁵N分配模式，决定了子实体相对于氮源的δ¹⁵N值。通过放射性碳测定，可将受试真菌分为心材定殖类群（拟层孔菌属（Fomitopsis）、猴头菌属（Hericium），其碳库年代约30年以上）与边材定殖类群（小菇属（Mycena）、盔孢伞属（Hypholoma）、栓菌属（Trametes），碳库年代为1~12年）。子实体的δ¹³C值较木材纤维素高0‰~2.5‰，这一现象可归因于组成差异、对部分¹³C富集的半纤维素（Hemicellulose）或蔗糖（Sucrose）的同化作用，以及代谢过程中的碳同位素分馏（¹³C Discrimination）。本研究的核心发现包括：(1) 木材腐朽真菌的碳、氮获取策略存在类群间差异；(2) 经热解气相色谱-质谱联用仪（Pyrolysis-GC-MS）分析，不同真菌类群的化学组成差异显著；(3) 真菌的碳库年代跨度为1年（小菇属Mycena）至30年以上（拟层孔菌属Fomitopsis、猴头菌属Hericium）；(4) 猴头菌属（Hericium）可优先同化¹³C富集的半纤维素；(5) 戊糖中脱除¹³C贫化的C6原子，是半纤维素δ¹³C值偏高的原因；(6) 不同真菌类群在子实体、菌丝体、蛋白与非蛋白组分间的氮分配模式存在差异。基于上述测定结果，本研究深化了对真菌同位素组成调控机制的定量与概念认知，明确了碳氮源、化学组成与代谢过程如何决定真菌的同位素组成。