Nezu Phytol.(1996), 133, 217-224 Nickel-accumulating plants from the ancient serpentine soils of Cuba BY R. D. REEVES1, A. J. M. BAKER2, A. BORHIDI3 AND R. BERAZAIN4 Department of Chemistry,Massey University,Palmerston North, New Zealand 2Department of Animal and Plant Sciences, Universityof Sheffield,UK 'Botanical Department,Janus Pannonius University,Pe'cs, Hungary 4Jardz'nBota'nico Nacional, Havana, Cuba (Received 17 July 1995; accepted 15 December 1995) SUMMARY Extraordinary uptake of nickel (Ni), reaching concentrations of 0 1-5 0 00, c. 1000 times greater than those usually found in flowering plants, has been observed previously in c. 190 species that grow on Ni-rich serpentine soils derived from ultramafic rocks in various parts of the world. These so-called hyperaccumulators of Ni include c. 50 species from the rich ultramafic flora of New Caledonia and c. 80 species from the Brassicaceae of Mediterranean Europe and Turkey. A study of a limited part (the families Buxaceae and Euphorbiaceae) of the very large ultramafic flora of Cuba has now identified this as the home of at least 80 hyperaccumulators, the largest number yet found in any one country. The more frequent incidence here of this unusual form of plant behaviour is linked to the very long period (c. 10-30 million years) during which some of the Cuban ultramafic substrata are believed to have been continuously available for colonization; the distribution of Ni hyperaccumulators between older and younger ultramafic soils in Cuba mirrors the overall incidence of endemic species in these areas. Key words: Nickel hyperaccumulators, ultramafic flora, serpentine soils, Buxaceae, Euphorbiaceae. rarityof any intermediate behaviour towards Ni, i.e. INTRODUCTION most plants on serpentine fall clearly into the Nickel concentrations in leaves of plants normally lie 'normal' (< 100 ,ag g-1 Ni) or 'hyperaccumulator' in the range 0 5-10 ,g g-1 on a dry matter basis. On (> 1000 ,ag g-1 Ni) categories, and (ii) the likelihood serpentine and other magnesium- and iron-rich that such an inordinate uptake of an element known (ultramafic) soils, which generally contain 500- to have deleterious effectson many enzyme systems 5000 ,g g-1 Ni, plants often show slightly elevated must be associated with distinctive detoxification Ni concentrations, in the range 5-100 ,g g-1. How- mechanisms within the plant. Studies of the metab- ever, a small proportion of those plant species that olism of Ni hyperaccumulators are still at an early tolerate ultramafic soils (no more than 1-2 0 world- stage, and the biochemical processes by which the Ni wide) show extreme Ni accumulation, reaching more is absorbed, transported and sequestered are not well than 10000 ,g g-1 (1 %o) in some cases. This type of understood. In the meantime, however, these plants behaviour was firstdiscovered in Alyssum bertolonii should not be regarded as mere curiosities: since in Italy (Minguzzi & Vergnano, 1948). The term most of them are endemic to Ni-rich soils they are hyperaccumulator (Brooks et al., 1977; Reeves, obviously of value as metal indicators, they might 1992) has been applied to plant species in which a Ni have important information to impart about evol- concentration above 1000 ,ag g-1 has been recorded ution in a number of plant genera and families, and in above-ground tissue of plants growing in their their genetic material might be of value in any natural habitat. Detailed studies and analytical work situation where enhanced plant uptake of metals is on plant tissue of specimens from serpentine soils in desired. many parts of the world during the last 20 yr have Several areas of the world where ultramafic rocks revealed that about 190 species (in more than 60 are important have not been studied in any detail differentgenera) behave in this way (Reeves, 1992). from a biogeochemical point of view. These include Justificationfor recognizing hyperaccumulation as Cuba, New Guinea and a number of islands of the a distinct form of plant response comes from (i) the Philippines and Indonesia. The ultramafic flora of 218 R. D. Reeves and others Habana- Camarioca- Campo Florido San Miguel \ anasi-Corral/Mtmo-- Sierradel \ Nuevo / / Santa Clara ^U Rosario ~~~~~~~Camaguey Cajalbana 20 - SJ~~~~~~~~~~~~~~Hogf 8 ~~~~~~~~~~~~~~~~~~~Moa-Baracoa Figure 1. Map of Cuba showing (in black) major regions of ultramafic soils. Bars opposite each region represent the total numbers of plant species endemic to each area (stippled bars) and the number of nickel hyperaccumulators found in each (solid bars) Scale at lower left. Cuba was of particular interestto us for several representedin Cuba (37 species, of which 30 are reasons. Extensive recent work on Cuban phyto- serpentine-obligate);Leucocroton is a genus endemic geography (Borhidi, 1991 a) has emphasized the to Cuba and Hispaniola, 28 of the 30 species being importanceof the Cuban ultramaficsoils as centres endemic to the serpentinesoils of Cuba; another of diversityand endemism. There is a remarkable genus of the Euphorbiaceae, Phyllanthus,has fur- similarityin geography,climate, tropical latitude nished hyperaccumulatorsin other parts of the and economic importance of ultramaficgeology tropics (New Caledonia, Sabah and the Philippine between Cuba in the North Hemisphere and New islands of Palawan and Mindanao) (Kersten et al., Caledonia in the Southern Hemisphere; the large 1979; Jaftr6,1980; Bakeret al., 1992) and is also well number of endemic species (and nickel hyper- representedin Cuba (53 taxa, of which49 are native accumulators) associated with the ultramaficsof and 39 are endemic,26 are serpentine-endemicand New Caledonia have been well documented(Jaffre & nine othersare serpentine-tolerant). Schmid,1974; Jaffreet al., 1976; Brookset al., 1977; Serpentinerocks underlie c. 70 ofthe land area of Jaffreet al., 1979a; Jaffre,Brooks & Trow, 1979b; Cuba. In the lowland-collinebelt of central Cuba Jaffre,1980), and it appeared likelythat because of thereare eightimportant serpentine areas, occupying many similarities of soil type and climate, Ni 2700 km2,between Sierra del Rosario and Holguin hyperaccumulationmight be a featureof the Cuban (Fig. 1). These surfacesare believed to have been ultramaficflora also. A previous study (Berazain, exposed relativelyrecently (Zonn, 1968), giving 1981) of the elemental composition of six Cuban fewerthan 1 million years for the developmentof serpentine plant species from Loma Galindo, their magnesian sialitic and ferraliticsoils and the Matanzas Province, showed that two of them, vegetation they support. By contrast,four other reported as Buxus flaviramea (Britt.) Mathou areas, 4800 km2in total, at the western(Caj'albana) (Buxaceae) and Leucocrotonflavicans Muell. Arg. and eastern(Nipe, Cristal,Moa-Baracoa) extremities (Euphorbiaceae)were hyperaccumulators, with maxi- of the island, have undergone soil and vegetation mum Ni concentrationsof 4500 and 7700,ag g-' developmentover a much longer period, perhaps respectivelyin the dry matter(63 %0 and 11 5 %0 in 10-30 millionyears (Finko, Korin & Formell,1967). the inorganic ash). The specimens of the former The longer period of evolution of these mature species are now identifiedas B. gonoclada (Wr. ex oxisols has led to a much higherfloristic diversity Griseb.) Muell. Arg., whereasthe specimensof the than is presenton the youngersoils. latterare now identifiedas L. angustifolius(Muell. Of the total Cuban floraof 6375 species, approx. Arg.) Pax & Hoffm. half are endemic to the island, and c. 300 of these It appeared that a search for furtherNi hyper- (920 species) are endemicto theserpentine soils. The accumulatorsin the Cuban florashould startwith influenceof thesesoils as a factorin the development the Buxaceae and Euphorbiaceae. Buxus is strongly of such a stronglyendemic flora is thereforewell out Ni-accumulating plants from Cuba 219 of proportion to the land area occupied. The 'young' clear that the genus includes 16 new hyperaccumu- serpentine areas, accounting for 36 % of the total lators of nickel in addition to the one previously serpentine soils, have provided only 140 of the reported. Of the species in Table 1, B. acuminata, B. serpentine endemic species, whereas the 'old' soils brevipes,B. cubana and B. sclerophylla are found on contain 81 00; the other 5 0 are common to both. limestone substrata and show the expected low Ni The number of species endemic to individual concentrations. The plants on serpentine show a serpentine areas is also illustrated in Figure 1. gradation in Ni uptake from low-normal values (2-50 ,g g-1) in species such as B. acunae, B. jaucoensis, B. leoni and B. wrightii,to high-normal MATERIALS AND METHODS values (50-150 ,ag g-1), particularly in the rain forest and mossy forestspecies such as B. marginalis and B. In the course of the present work, leaf fragments muelleriana, and finallyto the 17 hyperaccumulators from c. 120 species of the Buxaceae and Euphor- (> 1000 ,ag g-1). The presence of similar numbers of biaceae that occur commonly or exclusively on non-accumulators and hyperaccumulators among serpentine were screened for Ni accumulation by a the serpentine endemics in this genus should aid in simple semi-quantitative test using filter paper the tracing of evolutionary relationships among the impregnated with dimethylglyoxime (1 00 solution species. Of the 17 hyperaccumulators, eight are in ethanol). In cases of strong positive tests, and in endemic to the serpentines of the Moa-Toa-Baracoa other cases involving serpentine endemic species or area and three others to either the Cristal or Nipe non-serpentine species of genera with a strong areas, whilst three more are found in at least two of affinityfor serpentine, small portions of leaf (from these 'older' eastern regions. The remaining three herbarium specimens or from field collections) were are found on the younger serpentine soils of Holguin analysed by atomic absorption (AA) or ICP-emission (B. heterophylla), Canasi and Camarioca (B. gono- spectroscopy. From herbarium specimens, leaf sam- clada), and Motembo and Santa Clara (B. flav- ples of < 30 mg were generally used, to minimize iramea).