Intra- and inter-tree variability of the 87Sr/86Sr ratio in apple orchards and its correlation with the soil 87Sr/86Sr ratio

The 87Sr/86Sr ratio of horticultural products mostly derives from that of the bioavailable Sr fraction of the soil where they grow and, therefore, varies according to the local geolithological features. This study investigated the intra- and intertree variability of the 87Sr/86Sr ratio in two apple orchards in South Tyrol and its relation with the soil 87Sr/86Sr ratio. In both orchards, a moderate homogeneity of the 87Sr/86Sr ratio was observed among subsamples of the same tree part (shoot axes, leaves, apple peels, and pulps). Moreover, the 87Sr/86Sr ratio homogeneity among tree parts was high intratree and low intertree. The variability of the 87Sr/86Sr ratio within the tree and within the orchard is explained in light of the 87Sr/86Sr ratios of the soil. This 87Sr/86Sr variability within orchards does not preclude its use as a geographical tracer; however, this aspect should be evaluated to correctly design a sampling campaign or to generalize the results.