Ecology of nickel hyperaccumulator plants from ultramafic soils in Sabah (Malaysia)

Abstract

Sabah (Malaysia) has one of the largest surface expressions of ultramafic rocks on Earth and in parallel hosts one of the most species-rich floras. Despite the extensive knowledge of the botanical diversity and the chemistry of these substrates, until recently the records for nickel (Ni) hyperaccumulator plants in the area have been scant. Recent intensive screening has resulted in 19 new records, adding to the 5 previously known from Sabah. The results of this study indicate that most Ni hyperaccumulator plants in Sabah are restricted to successional habitats (ridges, river banks, secondary vegetation) at elevations <1200 m a.s.l. Moreover, Ni hyperaccumulators are locally common both in terms of number of individuals and relative number of species. Nickel hyperaccumulation occurs most frequently in the Order Malpighiales (families Dichapetalaceae, Phyllanthaceae, Salicaceae, Violaceae), and is particularly common in the Phyllanthaceae (genera Phyllanthus, Glochidion). Comparison of soil chemistry with elements accumulated in hyperaccumulator foliage showed significant correlation between soil exchangeable Ca, K, P and the foliar concentrations of these elements. No direct relationship was found between soil Ni and foliar Ni, although foliar Ni was negatively correlated with soil pH. Nickel hyperaccumulation has been hypothesised to fulfil herbivory protection functions, but extensive herbivory-induced leaf damage on Ni hyperaccumulators in Sabah was common, and specialist (Ni-tolerant) insect herbivores were found on several species in this study. The identification of Ni hyperaccumulators is necessary to facilitate their conservation and potential future utilisation in Ni phytomining.