Linking fungal communities to wood density loss after 12 years of log decay.

Changes in biodiversity might alter decomposition processes and, consequently, carbon and nutrient cycling. We examined fungal diversity and density loss in experimental Norway spruce logs after 12 years of decay in a hemiboreal forest. Between 28 and 50% of the original wood biomass remained, depending on the fungal community composition in the log, operational taxonomic unit (OTU) richness had only a minor effect on the log biomass. Although the communities were OTU rich (190-340 OTUs per log), the majority of OTUs were infrequent or rare; wood degradation therefore depended mostly on the most abundant OTUs and their decomposing abilities. The least decayed logs were characterized by continuous dominance of an earlier colonizer and by high within-log community diversity, which was significantly related to sample variables (position in log, density and moisture). In the most decayed logs, the earlier colonizers were generally replaced by white-rot species able to exploit the highly decomposed wood. The communities were relatively spatially uniform within whole logs, independent of the sample variables, whereas among-log diversity was high. Importance of fungal community composition in decomposition processes should be taken into account when studying and modeling carbon dynamics in forest ecosystems.

Diverse ecological roles within fungal communities in decomposing logs of Picea abies.

Fungal communities in Norway spruce (Picea abies) logs in two forests in Sweden were investigated by 454-sequence analyses and by examining the ecological roles of the detected taxa. We also investigated the relationship between fruit bodies and mycelia in wood and whether community assembly was affected by how the dead wood was formed. Fungal communities were highly variable in terms of phylogenetic composition and ecological roles: 1910 fungal operational taxonomic units (OTUs) were detected; 21% were identified to species level. In total, 58% of the OTUs were ascomycetes and 31% basidiomycetes. Of the 231 337 reads, 38% were ascomycetes and 60% basidiomycetes. Ecological roles were assigned to 35% of the OTUs, accounting for 62% of the reads. Wood-decaying fungi were the most common group; however, other saprotrophic, mycorrhizal, lichenized, parasitic and endophytic fungi were also common. Fungal communities in logs formed by stem breakage were different to those in logs originating from butt breakage or uprooting. DNA of specific species was detected in logs many years after the last recorded fungal fruiting. Combining taxonomic identification with knowledge of ecological roles may provide valuable insights into properties of fungal communities; however, precise ecological information about many fungal species is still lacking.