Effects of Nickel on Growth and Nutrient Concentrations in a Serpentine Endemic Cunoniaceae

ABSTRACT

Plants growing on serpentine soils are usually assumed to be nickel (Ni)-tolerant species. The objective of the work reported here was to find out whether Cunonia macrophylla Brongniart & Gris, an endemic species common on Ni-rich soils in New Caledonia, is indeed Ni tolerant. In a greenhouse experiment, plants were watered with solutions containing Ni chloride (5 to 1000 mg Ni L⁻¹) for 15 months before their morphological characteristics were measured, and the levels of nitrate, protein, and nutrients in the plants were determined. The plants grown with 5, 10, 50, and 100 mg Ni L⁻¹ had more leaves, and there was a tendency toward greater stem thickness and fresh shoot biomass at 50 mg Ni L⁻¹. Manganese (Mn), copper (Cu), and zinc (Zn) concentrations were also higher in the presence of 50 mg Ni L⁻¹. One thousand mg Ni L⁻¹ induced symptoms of Ni toxicity, and this effect may account for the lower concentration of potassium (K) in the shoots and roots of plants exposed to this concentration, as well as for inducing higher concentrations of soluble protein in the shoots. Calcium (Ca) and iron (Fe) levels were lower in roots exposed to higher concentrations of Ni. Nickel concentrations in the plant as a whole increased with the level of Ni applied, and the Ni gradient decreased from roots to stem and from stem to leaves. It was concluded that Cunonia macrophylla is a Ni-tolerant species that accumulates Ni without any impairment of growth when exposed to levels of up 500 mg Ni L⁻¹.

Keywords:

• Cunoniaceae
• New Caledonia
• macronutrient
• micronutrient
• plant physiology
• serpentine
• Ni

ACKNOWLEDGMENTS

Our thanks are due to the Southern Province of New Caledonia for its financial support. We would like to thank Drs. Colin and Duprey (I.R.D., Nouméa) for providing the facilities for mineral analyses. We also thank H. Fortune-Hopkins, who helped in the preparation of this manuscript.