LAUSR

BACKGROUND AND AIMS The aim of this study was to test the frequency distributions of foliar elements from a large dataset from Kinabalu Park (Sabah, Malaysia) for departure from unimodality, indicative of a distinct ecophysiological response associated with hyperaccumulation. METHODS We collected foliar samples (n = 1533) comprising 90 families, 198 genera and 495 plant species from ultramafic soils, and foliar samples (n = 177) comprising 45 families, 80 genera and 120 species from non-ultramafic soils and corresponding soil samples (n = 393 from ultramafic soils and n = 66 from non-ultramafic soils) from Kinabalu Park (Sabah, Malaysia). The data were geographically- (Kinabalu Park) and edaphically- (ultramafic soils) constrained. The inclusion of a relatively high proportion (~14%) of samples from hyperaccumulator species (with foliar concentrations of Al, Ni >1000 μg g-1, Co, Cu, Cr, Zn >300 μg g-1 or Mn >10 mg g-1) allowed for hypothesis testing. KEY RESULTS Frequency distribution graphs for most elements (Ca, Mg, P) were unimodal, although some were skewed left (Mg, Mn). The Ni frequency distribution was bimodal and the separation point for the two modes was between 250-850 μg g-1. CONCLUSIONS Accounting for statistical probability, the established empirical threshold value (>1000 μg g-1) remains appropriate. The two discrete modes for Ni indicate ecophysiologically distinct behaviour in plants growing in similar soils. This response is in contrast with Mn, which forms the tail of a continuous (approximately log-normal) distribution, suggestive of an extension of normal physiological processes.