Biodiversity and ecology of Tuber species in Mediterranean forest ecosystems of Sardinia

The genus Tuber comprises hypogeous fungi found in a wide range of habitats worldwide. These fungi form ectomycorrhizal symbiotic relationships with a variety of host plants, contribute to ecosystem health and biodiversity by promoting nutrient cycling, carbon sequestration and the resilience of forest communities. Species in this genus produce hypogeous edible ascomata commonly called truffle, sought by wildlife and humans. The ecology and geographic distribution patterns of Tuber species remain partially unknown due to the hidden nature of their hypogeous fruiting, detectable by their aroma from different coevolved mammals or with the help of trained dogs. Investigating the environmental factors associated with the natural occurrence of truffles is crucial to acquiring key information for a deeper understanding of their ecological niches. These information and knowledge are indispensable to direct conservation and management efforts of natural truffle habitats and the associated ecosystems. This study aims to deepen our understanding of the ecological dynamics of ectomycorrhizal fungi (ECM), particularly species belonging to the genus Tuber within Mediterranean forest ecosystems in Sardinia. Mycorrhizal symbioses are fundamental in terrestrial ecosystems, contributing significantly to nutrient cycling, carbon sequestration, and the resilience of forest communities. Truffles are known for both their ecological role and economic importance, thereby acting as a catalyst for the adoption of sustainable forest management strategies. The main objectives of this study were to identify the environmental factors determining the presence and potential distribution of truffle species in Sardinia. The R package “fuNiches” was developed to analyze ecological niche overlaps between ECM fungi, with the aim of statistically identifying co-occurring indicator species. The ecological niche of Tuber borchii in Sardinia was also quantified and interpreted through the application of the MAXENT model, and the ecological niche of Tuber aestivum through the construction of an ensemble model. Additionally, a new species belonging to the Puberulum clade was characterized and here proposed as Tuber fractum (nom. prov.). The study area was delimited in Sardinia based on the ISPRA Nature Map, selecting twenty-four vegetation classes, favouring forest types and Mediterranean environments known to establish symbiotic relationships with hypogeous and epigeous fungi. Data on the occurrence of hypogeous fungi, specifically of the genus Tuber, were collected through field surveys conducted from November 2021 to November 2024, with the help of truffle dogs. A dataset of approximately six hundred specimens was thus compiled, distributed across six genera for a total of approximately twenty species. The results obtained confirm that environmental variables, vegetation and soil conditions of the study area, are responsible for the delicate balance necessary for the presence of these fungi. The analyses carried out reveal that Sardinian forests host truffle species of economic interest, which are part of a larger ectomycorrhizal fungal community of great ecological importance. This thesis provides a holistic framework for understanding the ecology of truffles in Mediterranean forest ecosystems, offering concrete data to promote sustainable forest management, ensuring the presence and persistence of these important species, while guaranteeing the health and resilience of forest ecosystems.