Deadwood provides habitat important for biodiversity, and its decomposition plays a vital role in carbon and nutrient cycling in forest ecosystems. Deadwood decomposition is primarily driven by wood-inhabiting fungi, and decay processes can be redirected when disturbance alters fungal community assembly. Japanese oak wilt (JOW) is a common disturbance agent in Japanese secondary broadleaf forests, causing rapid, landscape-scale dieback of large oak trees and generating pulses of deadwood accumulation in recent decades. JOW involves the fungal pathogen Dryadomyces quercivorus, vectored by the ambrosia beetle Platypus quercivorus. Pathogen attack may stimulate oak tree’s defense responses and lead to the accumulation of phenolic secondary metabolites, potentially imposing chemical constraints on fungal colonizers. This study explores how these polyphenols relate to fungal communities in infected trees and whether temperature moderates their effect on fungi.
This study was conducted across three sites in Japan (AOB in Miyagi, YMS in Kyoto, TAN in Miyazaki) by setting logs of Quercus serrata killed by JOW and apparently healthy stems as controls, and monitoring them over time. The setting and sampling were conducted in autumn 2016 with 20 wilt logs and 20 healthy logs per site. Wood samples for fungal community and wood property analysis were taken from the top and bottom sides of each log. To further investigate the tolerance of wood-rot fungi, we cultured 7 species commonly found on Q. serrata at eight temperature levels and two tannic acid concentrations and compared their hyphal growth.
At all three sites, wilt logs had higher polyphenol concentrations than healthy logs. PERMANOVA detected that fungal community composition were strongly structured by JOW (R2 = 0.04, p = 0.0001) and site (R2 = 0.10, p = 0.0001), whereas sampling position (top and bottom) was not significant. Canonical correlations analysis for each site further indicated that polyphenol concentration was a key factor only at TAN (the southernmost site). Mycelial growth experiment supported the heterogeneity: tannin effects were species-specific, with strong inhibition at 0.1% for some taxa, weak effects or slight stimulation at 0.01%, and temperature-dependent responses, including enhanced growth in high tannin in some species under high temperature conditions. These results suggest that JOW increases polyphenols and can impose chemical filtering on fungi colonizers, but the strength of filtering depends on site conditions and temperature.