An introduced tree species alters the assemblage structure and functional composition of wood-decaying fungi in microcosms

Although it is widely recognized that introduced plant species produce organic matter of different quality surprisingly little is known about how this influence the community structure of decomposers. Here, we investigated the effects of a commercial non-native tree species, lodgepole pine, on the community structure of wood-decaying basidiomycetes and the decomposition of deadwood in northern Sweden. We allowed an assemblage of wood-decaying fungi that occur naturally on pine to interact on fresh wood-discs of lodgepole pine and Scots pine, using microcosms. At the end of the experiment we measured the wood mass loss and calculated the area of the different species' domains as indicated by interaction zone lines between competing species. Fungal assemblage structure developed in a markedly different way on lodgepole pine compared to Scots pine. In addition to there being fewer species in the final fungal assemblage on lodgepole pine, fungal functional composition was different. White-rot fungi were more competitive and dominated on lodgepole pine, while brown-rot fungi dominated on Scots pine. We also found that the decay rate of lodgepole pine wood was slightly lower, although the underlying reason remains unclear. However, there was a significant positive relationship between the abundance of white-rot fungi and the wood mass loss of lodgepole pine, while no relationship was found between fungal functional group and the decay rate of Scots pine. We also found no relationship between species richness and wood decay rates. Our study reveals that a non-native tree species used in commercial forestry can alter the structure and functional composition of a saprotrophic wood-decaying fungal assemblage. Future studies are required to clarify the mechanisms behind the observed patterns and whether they apply to natural systems.