The relationship between tree species and wood colonising fungi and fungal interactions influences wood degradation

Deadwood is one of the main terrestrial carbon (C) pools and its decomposition is fundamental in biogeochemical cycles. As fungi are the main wood degraders, a study was carried out on deadwood-colonising fungal community changes as a function of host plants and wood degradation. Deadwood fungal communities were investigated in adjacent woody plantations of hybrid poplar, willow and black locust established in the early 2000 s and abandoned for fifteen years. Lying deadwood was estimated in the three plantations and wood decay (WD) visually assessed using a 3-class scale. Fungal colonization of wood samples was assessed using culture-based methods and identified with morphological and molecular features. Wood colonising fungal communities differed in composition both between host plants and WD classes (P < 0.001). Ligninolytic white rot fungal species (Basidiomycota) prevailed in black locust and poplar, where they co-colonised all three wood decay classes in association with soft rot fungal agents. In willow, Daldinia chilidiae, a ligninolytic ascomycete, co-colonised deadwood with fungal species associated with tree dieback (Botryosphaeriaceae); whilst soft rot fungi principally colonised the highest wood degradation class. Results showed high fungal preference towards tree species that was most evident in ligninolytic fungi. Moreover, different wood decay paths were deduced from fungal changes across the three wood degrading classes and the necromass distribution in those classes. The co-habitation of white rot and soft rot fungi in all the wood decay classes of poplar and black locust indicated a continuum decay process; whilst the prevalence of soft rot fungi in the almost decomposed class in willow, suggested sequential succession of primary and secondary phases in deadwood degradation. Wood degradation is influenced by plant species and the native fungal microbiome and is mediated by multiple biotic interactions and environmental factors, which supports the use of wood colonising fungi as indicators of forest ecosystem health.