The influence of forest surroundings on the soil fungal community of black truffle (Tuber melanosporum) plantations

Black truffles are a highly valued non-wood forest product. The success of truffle plantations is arousing the interest to establish orchards within forest settings. One main concern is that the forest may act as a source of ectomycorrhizal fungi that could displace Tuber melanosporum in plantations and impair truffle production. We studied the effects of host tree distance to the surrounding forest on T. melanosporum development and on the root-associated fungal community. Our research was carried out in a 5-year old holm oak (Quercus ilex) plantation established in an abandoned pasture surrounded by a Q. ilex forest in the Pyrenees. The spatial distribution of different fungal guilds as well as of T. melanosporum mycelium quantity and mating types frequency was correlated with the distance to the forest and the diameter of the trees. We found a higher relative abundance of non-T. melanosporum EcM fungi associated with the trees closer to the forest. Larger root collar diameter trees had greater biomass of T. melanosporum mycelium and displayed fungal community compositions less affected by the distance to the forest. No associations between the biomass of T. melanosporum mycelium in the soil and the distance to the forest or the abundance of non-T. melanosporum EcM fungi were observed. Our results indicate that T. melanosporum inoculated oaks planted in areas surrounded by forests may be colonised by other ectomycorrhizal species, and develop a distinct microbial community from those usually established in agricultural lands. Further investigations should be carried out to determine whether a different fungal community may affect truffle production in the future, but to date, truffle mycelium does not seem to be impaired.