Identifying environmental factors affecting the microbial community composition on outdoor structural timber.

Timber wood is a building material with many positive properties. However, its susceptibility to microbial degradation is a major challenge for outdoor usage. Although many wood-degrading fungal species are known, knowledge on their prevalence and diversity causing damage to exterior structural timber is still limited. Here, we sampled 46 decaying pieces of wood from outdoor constructions in the area of Hamburg, Germany; extracted their DNA; and investigated their microbial community composition by PCR amplicon sequencing of the fungal ITS2 region and partial bacterial 16S rRNA genes. In order to establish a link between the microbial community structure and environmental factors, we analysed the influence of wood species, its C and N contents, the effect of wood-soil contact, and the importance of its immediate environment (city, forest, meadow, park, respectively). We found that fungal and bacterial community composition colonising exterior timber was similar to fungi commonly found in forest deadwood. Of all basidiomycetous sequences retrieved, some, indicative for Perenniporia meridionalis, Dacrymyces capitatus, and Dacrymyces stillatus, were more frequently associated with severe wood damage. Whilst the most important environmental factor shaping fungal and bacterial community composition was the wood species, the immediate environment was important for fungal species whilst, for the occurrence of bacterial taxa, soil contact had a high impact. No influence was tangible for variation of the C or N content. In conclusion, our study demonstrates that wood colonising fungal and bacterial communities are equally responsive in their composition to wood species, but respond differently to environmental factors. KEY POINTS: • Perenniporia meridionalis and Dacrymyces are frequently associated with wood damage • Fungal community composition on timber is affected by its surrounding environment • Bacterial community composition on structural timber is affected by soil contact.