Jean Michele Ricard, who wrote what I do think is one of the best technical truffle guides (La truffe: Guide pratique de trufficulture, Ctilf) has been studying the relationship between grapes and truffle trees by DNA tools. He has seen how, although truffles can not form mycorrhiza with the grapes roots, its mycelium has been found in their roots (found for Tuber melanosporum, aestivum and brumale). So although it seems do not have an influence on truffle production, could have a functional role on truffle ecology. I guess that probably at the same level than other shrubs do (rosmary, thyme, Juniperus…).
It’s amazing to see that truffle mycelium, even in small trees, can be found quite far away from the tree, so exploring the soil and the neighbour shrubs around:
A paper from Liu et al, (Tuber melanosporum rapidly colonizes the soil surrounding its host tree in Quercus ilex plantations), study the amount of DNA found at different distances from the trunk of the tree. Its funny to see how a holm oak with 3 years has 1000 times more truffle mycelium at 40cm than at 1meter from the trunk. But at year 5, it is just 100 times more, and when the tree is 7 years old, there is no difference on the quantity of truffle mycelium at 40cm-1m or 2m from the trunk. So it seems there is a certain stage that the truffle mycelium seems to stabilize to a maximum. It could exist a maximum load capacity innthe soil, and beyond that no more mycelium is produced?
All the best,
marcos S. Morcillo