Tuber aestivum is associated with changes in soil chemistry and reduced biological quality in a Quercus pubescens stand in Northern Italy

Truffles contribute both directly and indirectly to important dynamics in the soil web, being involved in a large number of ecological functions that are crucial for terrestrial ecosystems. Despite this, the interrelationships between true truffles, i.e. hypogeous ectomycorrhizal fungi producing valuable fruiting bodies, and other elements of the soil system are largely unknown. In this study, we aimed to shed new light on whether and how much Tuber aestivum affects soil microbial activities (evaluated as enzyme activities), abundance (assayed as soil DNA content) and bacterial genetic diversity along with soil chemical properties. We compared chemical and biological variables inside and outside brûlés (i.e. areas inhabited by truffles with scarce vegetation cover around host plants) in two seasons, namely spring and summer, using both a linear mixed model and a multivariate two-block partial least squares approach. The areas with truffle presence had higher pH but lower organic carbon and nitrogen content. Similarly, all enzyme activities were lower inside the brûlé than outside, with the exception of peroxidase. A soil quality index (i.e. AI3) based on three enzyme activities (β-glucosidase, acid phosphomonoesterase and urease) indicated a reduction in soil quality inside the brûlé. Overall, soil DNA content responded to an interaction of truffle presence/absence and season, while bacterial genetic diversity indexes were higher in spring. Despite the observational nature of this study, results point out that T. aestivum can be considered a key species in the soil where it is present as it was associated with changes in chemistry as well as microbial activity that were generally more conspicuous than mere seasonal effects, although the causative nature of these associations still needs to be confirmed.