Intensive cycling of nickel in a New Caledonian forest dominated by hyperaccumulator trees

The hyperaccumulator Pycnandra acuminata is a New Caledonian rainforest tree known to have the highest concentration of nickel in any living organism, with 25 wt% nickel in its latex. All trees (with a diameter of >10 cm) and soil profiles in a 0.25-hectare permanent plot were sampled to assess the biogeochemical compartmentalisation of nickel in a dense stand of P. acuminata trees. Nickel stable isotope analysis permitted insights into the cycling of nickel in this ecosystem. The total tree biomass of the plot was calculated to be 281 tonnes ha⁻¹, which contained 0.44 kg of cobalt, 49.1 kg of manganese, 257 kg of nickel and 6.76 kg of zinc. Nickel stable isotope analysis identified the biotic origin of the nickel in the soil upper layers, with P. acuminata shoots enriched in lighter nickel isotopes. The δ⁶⁰Ni latex signature suggests that long-distance transport, radial xylem and phloem loading are at play in P. acuminata.