Contrasting patterns of nickel distribution in the hyperaccumulators Phyllanthus balgooyi and Phyllanthus rufuschaneyi from Malaysian Borneo.

Globally, the majority of Ni hyperaccumulator plant occur on ultramafic soils in tropical regions, and the genus Phyllanthus from the Phyllanthaceae family, is globally the most represented taxonomical group. Two species from Sabah (Malaysia) are remarkable because Phyllanthus balgooyi can attain over 16 Wt% of Ni in phloem exudate, while P. rufuschaneyi reaches foliar concentrations of up to 3.5 Wt% Ni which are amongst the most extreme concentrations of Ni in any plant tissue. Synchrotron X-ray fluorescence microscopy (XFM), nuclear microbe (micro-PIXE+BS) and (cryo) scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) were used to spatially resolve the elemental distribution in plant organs of P. balgooyi and P. rufuschaneyi. The results show that P. balgooyi has extraordinary enrichment of Ni in the (secondary) veins of the leaves, whereas in contrast in P. rufuschaneyi Ni occurs in interveinal areas. In the roots and stems Ni is localized mainly in the cortex and phloem but is much lower in the xylem. The findings of this study show that, even within the same genus, the distribution of nickel and other elements, and inferred processes involved with metal hyperaccumulation, can differ substantially between species.