Oak Wilt Disease May Reduce the Initial Decay Rate of Dead Quercus serrata Stems by Altering Fungal Communities in the Wood

Oak wilt causes severe dieback of Quercus serrata, a dominant tree species in the lowlands across Japan. This study evaluated the effects of oak wilt on the wood-inhabiting fungal community and the decay rate of deadwood using a field monitoring experiment. We analysed the fungal metabarcoding community from 1200 wood samples obtained from 120 experimental logs from three forest sites at five different time points during the initial 1.5 years of the experiment. Death due to wilt significantly influenced the fungal community composition and reduced fungal diversity, likely due to the dominance of a limited number of species. The operational taxonomic unit richness, occurrence frequency, and DNA copy number of white rot fungi were also enhanced on the logs killed by wilt, depending on the sites. Structural equation modelling suggested that the wilt-initiated changes in the fungal community reduced the decay rate of oak logs. Temperature and wood moisture also affected the fungal community and log decomposition. These results suggest that, in addition to the direct effect of climate, oak wilt indirectly affects log decomposition by structuring the fungal community. Continuous monitoring is essential to evaluate the longer-term effects of oak wilt on the fungal decomposition of wood.