Re-examination of the elemental composition of some Caryophyllaceae on North American ultramafic soils

A paper of Kruckeberg et al. (1993) reported the hyperaccumulation of nickel by Arenaria rubella at an ultramafic site at Olivine Bridge in the state of Washington, USA. Several aspects of the publication led the present authors to doubt the reliability of the data, leading to a reinvestigation of the behaviour of this species at this site. Extensive sampling of two species of the Caryophyllaceae, A. rubella and Cerastium arvense, was then carried out at Olivine Bridge in two different years, together with the collection of soil samples. The plant samples were treated in various ways in an attempt to reduce the potential influence of soil contamination. The results of this work indicate that A. rubella and C. arvense both behave in a normal way in respect of their nickel uptake from ultramafic soil. The elements nickel, iron, cobalt, chromium and magnesium have been found at levels only 1/10–1/100 of those reported in the earlier work. The weaknesses in the earlier study have led to a consideration of several aspects of putative nickel hyperaccumulation, especially as applied to species in the Caryophyllaceae. Particularly important are washing procedures, selection of material for analysis, and the use of various criteria for assessing the likelihood of soil contamination of plant samples. A careful re-examination of several other reported cases of nickel hyperaccumulation by members of the Caryophyllaceae is now recommended.