Resource utilization of wood-inhabiting fungi

Decomposition of dead wood, which is controlled primarily by fungi, contributes substantially to the long-lived forest carbon pool and has potentially a significant role in nitrogen cycling. Decay wood N content has been found to increase with advancing wood decay in several studies. The likely main mechanism has been considered to be translocation of soil N by nonunit-restricted wood-decay fungi. To examine the potential sources of external N we combined several analytical methods on decay wood from a Norway spruce (Picea abies [L.] Karst.) dominated forest, including culture-free DNA extraction and fungal amplicon sequencing with Illumina MiSeq platform. Substantial abundance of fungal species with the reported capability to form rhizomorphs or mycelial cords for soil scavenging was detected in many decay wood samples, which contain higher N content than expected from N2 fixation alone. Our results suggest transport of soil N to wood via wood-decay fungi at intermediate stages of decay and by mycorrhizal fungi at late stages of decay. However, N2 fixation was observed to have a major role in increasing N content of wood during decay peaking at class V with its ~60% share of total N accumulation.