Abstract
We investigated accumulation of elements (Ca, Co, Cr, Cu, Fe, K, Mg, Mn, P, Pb, and Zn) in leaves of different ages for 11 evergreen woody plant species from serpentine soils of New Caledonia. Species were classified into four categories of Ni accumulation ability: one species was a non-accumulator (<100 mg Ni/ kg), three were accumulators (100–1000 mg Ni/kg), two were hyperaccumulators (1000–10,000 mg Ni/kg), and five were hypernickelophores (>10,000 mg Ni/kg). We harvested leaves from each species, separating them into three (four in one case) relative age categories based upon their position along branches (younger toward the apex, older far from it). Leaf samples were dried, ground, and dry-ashed, and their elemental concentrations were determined by inductively coupled plasma spectrometry (all elements except Ni) or atomic absorption spectrophotometry (Ni). Great variation was found for most elements both within and among species, but Ni varied most (1050-fold between species for oldest leaves). Correlations between Ni and other transition metals showed no significant relationships within samples of any species, but, we found significant positive correlations between Ni and Pb (correlation coefficient = 0.97) and Ni and Fe (correlation coefficient= 0.87) among species. Leaf Ni concentrations varied significantly with leaf age for two species, the hypernickelophores Geissois pruinosa and Homalium kanaliense. We conclude that Ni concentration varies markedly between species, but generally does not vary with leafage within species. We also suggest that four Ni accumulation category terms— non-accumulator, hemi-accumulator, hyperaccumulator, and hypernickelophore—be used to subdivide the wide variation found in Ni concentrations in plant leaves.