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 b ed 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 - expr essed in terms of 0.25-2.00 mm aggregate fraction, total organic carbon, DT PA-extractable Mn and host plant height - and to determine if these modific ations, whenever present, could be ascribed to soil differentiation within the truffle bed. The occurrence of pianelli - i.e. areas with little herbac eous 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 increa sed absorption of nutrients related to the ectomycorrhizal partnership, but also to soil differentiation. The soils of the investigated area were char acterized by a relatively low slope gradient, a rigid framework of gravel a nd a homogeneous physico-chemical behaviour, due to the predominance of Ca among exchangeable bases. In these environmental conditions, T. melanosporu m 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 la tter case, the plant cover was probably too scarce to protect T. melanospor um from summer dryness, and consequently the more resistant T. aestivum spe cies prevailed.