Changes in the Wood Fungal Community Composition in Living Chamaecyparis pisifera Trees During the Progression of Heart Rot Caused by Serpula himantioides

Abstract

Serpula himantioides is a widely distributed wood rot fungus that causes heart rot in various tree species. In Japan, heart rot due to S. himantioides occurs in Chamaecyparis pisifera; however, changes in the wood fungal community composition accompanying the progression of heart rot in living trees remain unclear. In this study, we clarified the changes in the fungal community composition of heartwood as heart rot progresses by performing an amplicon sequence analysis using DNA samples collected from living C. pisifera trees with heart rot caused by S. himantioides. Additionally, the mode of decay progression was characterised according to non-hierarchical clustering. The composition of S. himantioides sometimes reached extreme levels as heartwood decayed. This result is consistent with the findings of a previous study on heartwood decay in broad-leaved tree logs. However, there was no clear relationship between fungal diversity and the decrease in wood density, which was inconsistent with the results of a previous study on logs. Thus, this inconsistency may be influenced by the highly selective environment within heartwood. A clustering analysis grouped samples into four clusters, and the trophic modes and wood saprotroph decay types of indicator operational taxonomic units (OTUs), which characterised each cluster, changed during the decay process. The indicator OTUs and environmental variables for each cluster revealed that the four clusters corresponded to the pre-decay and incipient, intermediate and advanced decay stages. The study findings may be useful for further elucidating the decay of living trees infected by wood rot fungi.