Calcareous amendments in truffle culture: A soil nutrition hypothesis

Several statistical studies have indicated that a high concentration of active carbonate in the soil favours Tuber melanosporum fruit body production. The amount of active carbonate is significantly higher and the total carbonate is significantly lower inside than outside the T melanosporum brules. These statistical patterns and other works show that T melanosporum mycelia may acidify their immediate soil environment and solubilise carbonated fractions. Subsequently, the particular environmental conditions of brule soils may favour a secondary carbonate precipitation with a net increase in active carbonate which would in turn favour T melanosporum mycelia. The greater brule size and fruiting are simultaneously both related to how well the fungus is growing, suggesting that the model which best explains the cause-effect of all these observations is a feedback process. Other statistical studies suggest that active carbonate favours increased fruiting of T melanosporum as compared with Tuber aestivum, Tuber mesentericum and Tuber rufum, which has led to the use of calcareous amendments in truffle culture. We have studied the carbonated fractions of 46 soil samples from T melanosporum plantations contaminated and uncontaminated with Tuber brumale (a serious problem in truffle culture), and it appears that the use of calcareous amendments does not serve to eradicate T brumale from these plantations. However, we have observed the positive effect of calcareous amendments on the production of fruit bodies of both species. The similar response by T melanosporum and T brumale to soil active carbonate may be related to the close phylogenetic relationships between both species. Based on these findings, we propose a new soil nutrition hypothesis as a guide for research procedures in truffle soil ecology. Soils which are high in active carbonate lead to host plant chlorosis, which is a symptom of an underlying nutrient deficiency. This nutrient deficiency could lead to greater colonisation of T melanosporum ectomycorrhizas and favour the growth of mycelia, fruit body production and brule development, which in turn encourages the formation of new amounts of active carbonate on the basis of the proposed feedback model. (C) 2009 Elsevier Ltd. All rights reserved.