Occurrence of Tuber melanosporum in relation to soil surface layer properties and soil differentiation

An intensive survey was carried out on a 12-year-old experimental truffle bed of Tuber melanosporum Vitt. located in the central Apennines. The aim of the investigation was to relate the presence and carpophore production of T. melanosporum to changes in soil structure, aeration and fertility - expressed in terms of 0.25-2.00 mm aggregate fraction, total organic carbon, DTPA-extractable Mn and host plant height - and to determine if these modifications, whenever present, could be ascribed to soil differentiation within the truffle bed. The occurrence of pianelli - i.e. areas with little herbaceous ground cover created by T. melanosporum - showed a close relationship with host plant height and aeration of soil surface layers. Where pianelli occurred, the height of symbiont trees increased and the content of reduced Mn, indicating the presence of a well-aerated soil environment, decreased. The variation of host plant height was attributable not only to the increased absorption of nutrients related to the ectomycorrhizal partnership, but also to soil differentiation. The soils of the investigated area were characterized by a relatively low slope gradient, a rigid framework of gravel and a homogeneous physico-chemical behaviour, due to the predominance of Ca among exchangeable bases. In these environmental conditions, T. melanosporum was present in the rather thick soil belonging to Typic Rendolls, whereas it was absent in the area characterized by thin Lithic Rendolls. In the latter case, the plant cover was probably too scarce to protect T. melanosporum from summer dryness, and consequently the more resistant T. aestivum species prevailed.