The wild-grown Boletus edulis (penny bun) mushroom from the granite-based substrate: Trace elements uptake and Mg, Cu, Zn, and Cd isotope fractionations

We studied trace element distributions (with the use of the Agilent Technologies 5110 ICP-OES) and Mg, Cu, Zn, and Cd isotope fractionations (with the use of the MC-ICP-MS Neptune, ThermoFisher) in a substrate (granite-based)-to-mushroom (Boletus edulis) system. B. edulis likely intakes elements only in amounts necessary for its healthy existence, almost regardless of the composition of the substrate. Significant isotope fractionations occur at the soil-to-mushroom interface (Δ values varied from −1.58 ‰ for Mg to +0.72 ‰ for Cd). B. edulis from the granite-based substrate preferentially took up a lighter Mg isotope, whereas heavier isotopes of Cu, Zn, and Cd are taken up preferentially. Within-mushroom isotope fractionations were not so strongly pronounced. The strongest extent of the within-mushroom isotope fractionation was observed for Mg (within-mushroom Δ²⁶Mg = −0.45 to +0.35 ‰) and Zn (within-mushroom Δ⁶⁶Zn = −0.33 to +0.40 ‰) whereas the weakest, for Cu (within-mushroom Δ⁶⁵Cu = −0.14 to −0.02 ‰) and Cd (within-mushroom Δ¹¹⁴Cd = −0.09 to +0.08 ‰). Mg and Zn isotope fractionations could be due to the physical properties of the mushroom. With no redox-related Cu isotope fractionation involved, kinetic processes and Cu⁺ complexation to S could lead to the observed subtle negative within-mushroom Cu isotope fractionation. Very insignificant Cd isotope fractionation can be due to still unidentified fungal-driven fractionation processes. Overall, the study conducted confirmed that B. edulis is able to uptake elements with different degrees of readiness and translocate them within the fruiting body with differing intensities subjecting the elements to isotope fractionation at different extent.