Changes in Mg-Cu-Zn isotopic features in a system red cracking bolete – soil over an extended period

Abstract

We studied Mg–Cu–Zn isotope systematics of the Xerocomellus chrysenteron mushroom samples collected during two consecutive growing seasons from three sites underlain by granite, amphibolite, and serpentinite bedrock. None of the elements analyzed in mushrooms (Mg, Cu, Zn) displayed site-dependency in concentrations. The studied soils were depleted in ²⁶Mg isotope (δ²⁶Mg = −0.78 to −0.30‰) and displayed a very wide range of δ⁶⁵Cu values (−0.85 to +0.67‰). Values of δ⁶⁶Zn were mostly negative for soils from the granite-based site (−0.33 to +0.07‰), positive for soils from the amphibolite-based site (+0.03 to +0.12‰), and only slightly deviated from zero for soils from the serpentinite-based site (−0.09 to +0.09‰). Observed difference in isotope compositions between the mushroom-bearing and mushroom-free soils was most likely due to the presence of mushroom's mycelium in the mushroom-bearing soils. Isotopes of Mg, Cu, and Zn fractionated to different extent during both uptake and within-mushroom translocation. Mushrooms displayed higher uptake of isotopically light Mg (Δ²⁶Mg_FB-soil = −0.71 to −0.12‰), isotopically heavy Zn (Δ⁶⁶Zn_FB-soil = 0.61–0.91‰), and isotopically variable Cu (Δ⁶⁵Cu_FB-soil = −1.22 to +1.03‰). The ranges of the within-mushroom isotope fractionation were significant: Δ²⁶Mg displayed a total range of values of 1.09‰; Δ⁶⁵Cu, of 0.65‰; and Δ⁶⁶Zn, of 0.38‰. No uniform scheme of the within-mushroom isotope fractionation was observed for any studied element.