Snapshot of a vineyard: how do long-term agronomic practices influence soil bacterial and fungal diversity?

Vineyard soils are often characterized by excessive metal concentrations due to the long-term application of metal-containing pesticides. However, the total concentration is not always correlated with the bioavailable fraction of metals since it is a function of the chemical, physical and biological edaphic properties. Furthermore, the metal distribution within a vineyard surface is most likely very heterogeneous changing from row, the area between the rows (here named inter-row) and headland. Indeed, the aim of this study was to assess how the microbial diversity is affected by metal gradients within a vineyard. A total of 27 soil samples were collected, choosing three different sites: row, inter-row and headland. The soils were chemically characterized, then the microbial community was assessed by metabarcoding of 16SrRNA gene (for bacteria) and ITS region (for fungi). The results show that, as expected, the soil samples collected in row and in inter-row are chemically different from the headland soil, exhibiting this latter a significant lower concentration of heavy metals. This uneven distribution drives microbial communities with copper, total organic carbon and total nitrogen as main players. It is interesting to note that bacterial and fungal alpha-diversity do not change among the sites. On the contrary, the beta-diversity is affected by the chemical gradient. Thus, heavy metals do not seem to affect the total soil alpha-biodiversity but clearly drive the microbial composition (beta-diversity). These microbial shifts within microhabitats should be further investigated in order to verify if the stress can promote some specific pathogenic and/or beneficial fungal and bacterial taxa representing then, in a long-period vision, a serious risk for the viticulture in vocated areas.