Statistical patterns of carbonates and total organic carbon on soils of Tuber rufum and T. melanosporum (black truffle) brûlés

The ascocarps of several truffle species, such as Tuber rufum, are harvested in T. melanosporum brules; these species reduce T. melanosporum production. Some authors argue that this competition might be due to the evolution of organic matter in the soil. However, soil conditions in brules have yet to be clarified, and most studies on T. melanosporum fail to supply statistical data. We propose a study of 40 soils to compare the values for total organic carbon (TOC), pH, and carbonates inside the brules with the values for the outer edges of the same brules, where T. rufum ascocarps are collected. A principal component analysis relates the soils from the inner brules with high active carbonate content and soils outside the brules with high TOC and total carbonate content. ANOVA analyses indicate that the mean concentration of active carbonate, total CO32–, and % active/total carbonate differ significantly depending on soil location, but there are no significant differences for pH and TOC. These results lead us to propose a new hypothesis: T. melanosporum mycelia may solubilise active carbonate ( 50 μm) inside the brules; however the environmental conditions of the brules could favour a secondary carbonate precipitation with a net increase in active carbonate. This increase would counterbalance carbonate losses from leaching, which would in turn favour T. melanosporum mycelia, suggesting a feedback process.