Niche construction by two ectomycorrhizal truffle species (Tuber aestivum and T. melanosporum)

Niche construction by biota has been frequently reported for animals and plants, but fungi have received less attention. For mycorrhizal fungi, mutualistic niche construction has been proposed where partners construct niches for each other. However, few eco-evolutionary mechanisms leading to mutualistic symbiotic feedback have been described. Here we report niche construction by two ectomycorrhiza-forming species of truffles, Tuber aestivum and T. melanosporum. The soils of 263 spots of these Tuber, which create bare patches (brûlés), have been monitored (9–10 years) in natural forests to analyze whether they meet the criteria to satisfy the mutualistic niche construction process. Soil habitat modification by these Tuber can be seen in their brûlés, where the vegetation of arbuscular mycorrhizal plants and soil organisms are largely suppressed. Tuber melanosporum brûlés were smaller more productive, and with lower vegetation cover than T. aestivum. Interactions among soil carbonates, pH, and brûlé size are associated with increased carpophore productivity, indicating positive feedback between habitat modification and fungal fitness. Both species modified the habitat differentially. Tuber aestivum brûlés had higher pH and lower total carbonate than soils outside. Tuber melanosporum brûlés had lower total carbonate and higher exchangeable Ca²⁺ and active carbonate than soils outside. In conclusion, brûlés show a mutualistic niche construction process because modifies their soil environment and increases the fitness of both Tuber spp. Enhanced carbonate weathering by truffles resulted in lower soil quality with a negative impact on plants, indicating that mutualistic niche construction does not equally benefit both partners.