Abstract
Besides their symbiotic association with tree rootlets, ectomycorrhizal (EM) fungi have been commonly detected in nature in deadwood and plant debris of various tree species. However, their potential dual roles as symbiotrophs and saprotrophs are still debated. Here, we provide evidence from a series of experiments on the plasticity of symbiotrophic-saprotrophic lifestyles of the ectomycorrhizal fungus Piloderma croceum associated with Quercus robur L. Specifically, we find that P. croceum efficiently colonizes deadwood of oak in an experimental system without living oak. Results based on the productions of hydrolytic enzymes and corticrocin as well as the (14)C content in deadwood and mycelium of P. croceum demonstrate its capability of wood decomposition and assimilation of C from the decomposing wood. Our results also show that in presence of wood pieces colonized by saprotrophic mycelium of P. croceum, the roots of oak plants develop true EM symbiosis with Hartig net formation. Collectively, our results indicate a role for mycelium growing in deadwood as an underestimated EM fungus propagule bank, suggesting that deadwood and other decomposing plant material may indirectly influence the productivity of forest ecosystems by contributing to the recruitment of mycorrhizal fungi, thereby enhancing plant nutrient acquisition.