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

Globally, the majority of Ni hyperaccumulator plants 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 >16 wt% of Ni in its phloem exudate, while Phyllanthus 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, nuclear microbe (micro-PIXE+BS) and (cryo) scanning electron microscopy with energy dispersive spectroscopy were used to spatially resolve the elemental distribution in the 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.

Automated summary

Nationally, most hyperaccumulator plants that contain high levels of nickel are found in tropical regions with ultramafic soils. Phyllanthus, a taxonomical group from the Phyllanthaceae family, is the most commonly represented genus globally. Two species from Sabah, Malaysia, are particularly notable as Phyllanthus balgooyi can secrete more than 16% nickel in its phloem exudate, while Phyllanthus rufuschaneyi reaches foliar concentrations of up to 3.5% nickel, which are among the highest concentrations found in any plant tissue. Advanced imaging techniques were used to study the element distribution in various plant organs of P. balgooyi and P. rufuschaneyi. The results showed that P. balgooyi has a remarkable enrichment of nickel in the veins of its leaves, while in contrast, P. rufuschaneyi has nickel mainly occurring in interveinal areas. The study highlights the significant differences in the distribution of nickel and other elements between species, even within the same genus.