Nickel hyperaccumulation in populations of Psychotria grandis (Rubiaceae) from serpentine and non-serpentine soils of Puerto Rico

Abstract

Metal hyperaccumulators are plants that store heavy metals or metalloids in their leaves, often to concentrations much higher than in the soil. Though most occur exclusively on metalliferous soils, some species are facultative, occurring on both metalliferous and nonmetalliferous soils. Psychotria grandis Sw.(Rubiaceae) occurs from Central America through the Caribbean on many soil types, and hyperaccumulates nickel (Ni) on serpentine soils in several localities. In this study, four Puerto Rican populations of P. grandis – two from serpentine soil and two from non-serpentine soil – were examined to compare Ni accumulation between and within populations. Multiple trees were sampled at most sites, with replicate leaves harvested from each tree. Foliar nickel concentrations were measured by atomic absorption spectrometry. Mean Ni concentration differed significantly among the sites, ranging from <165 µg g–1 on non-serpentine soil to >4000 µg g–1 on serpentine soil. There were also significant differences in Ni concentration among trees within sites, with especially wide variation at one of the serpentine sites known to be geologically heterogeneous. Despite these differences in field-collected leaves, a hydroponic common-garden experiment indicated that the Ni accumulation capacities of the populations were approximately equal. Variation in Ni accumulation between and within these populations in the field is likely to result from variation in Ni availability in the soil.

Phylogenetic and geographic distribution of nickel hyperaccumulation in neotropical Psychotria

“…Studies of P. grandis in Puerto Rico have shown that the species occurs on both ultramafic (high‐Ni) and non‐ultramafic (low‐Ni) soils. As expected, foliar Ni concentrations reached the hyperaccumulation threshold of 1000 μg/g only on ultramafic soils (Campbell et al., ; McAlister et al., ).…”

“…In most cases, research has shown that facultative hyperaccumulators possess the underlying biological mechanisms for hyperaccumulation in all populations of the species, regardless of soil type, though they cannot exhibit a hyperaccumulator phenotype on nonmetalliferous soil (Pollard et al., ). A previous study (McAlister et al., ) provided tentative evidence for such species‐wide hyperaccumulation ability in P. grandis ; however, the physiology and population biology of P. costivenia have not been studied in relation to hyperaccumulation.…”

“…A set of 261 calibration samples were prepared, with each sample consisting of a 20 × 20 mm square of leaf lamina. Calibration samples were intended to cover a wide range of Ni concentrations and included multiple samples of a known Ni hyperaccumulator ( Psychotria grandis ) from both ultramafic and non‐ultramafic soils in Puerto Rico (McAlister et al., ), along with samples of six other species from various sites North and South Carolina, United States, including the Buck Creek ultramafic barren (Pollard, ) and other more typical soils.…”

Global Distribution and Ecology of Hyperaccumulator Plants

“…Following initial observations by Berazaín (1981), a survey of much of the Caribbean ultramafic flora revealed 128 such species in Cuba, as well as Phyllanthus nummularioides from the Dominican Republic (Reeves et al 1996(Reeves et al , 1999. Psychotria grandis is a Ni hyperaccumulator where it occurs on ultramafic soils in Puerto Rico (Reeves 2003;Campbell et al 2013;McAlister et al 2015). Other major sources of Ni hyperaccumulator plants, with more than 50 species each, are New Caledonia (see Fig.…”

Global research on ultramafic (serpentine) ecosystems (8th International Conference on Serpentine Ecology in Sabah, Malaysia): a summary and synthesis

“…It is, however, a rare phenomenon, with only 1-2% of plant species found on ultramafic soils displaying this behaviour. A smaller but increasing number of plants are known as 'facultative hyperaccumulators,' hyperaccumulating heavy metals only when occurring on metal-rich soils, but also occurring commonly on normal, non-metalliferous soils McAlister et al 2015). Currently,~450 nickel (Ni) hyperaccumulators are known (van der Ent et al 2013a).…”