Saprotrophic versus symbiotic strategy during truffle ascocarp development under holm oak. A response based on C-13 and N-15 natural abundance

The development of truffles in the soil is not well understood. It is not known if a direct transfer of carbohydrates takes place between the host tree and the developing ascocarps through ectomycorrhizal structures or whether sporophores become independent from their hosts after several weeks or months and are able to use dead host tissues or soil organic matter as carbon (C) and nitrogen (N) sources. To study saprophytic or symbiotic capacities of truffle ascocarps the natural abundance of N-15 and C-13 in foliage, wood, fine roots, mycorrhizae, fungal sporophores and soil were determined in a truffle orchard. The processes of carbon and nitrogen allocation remained unchanged during the entire period of ascocarp development of Tuber melanosporum. From C-13 and N-15 natural abundance measurements, T. melanosporum, T. brumale and T. rufum did not exhibit saprotophic strategy during ascocarp development, which is contradictory to common statements found in handbooks regarding truffle cultivation.