Toxicity of metals in plants. II. Characterization of Nickel toxicity in coffee

Abstract

The objective was to determine and characterize toxicities of Ni in coffee (Coffea arabica L., cv. Catuai Vermelho) seedlings growing in solution culture with different amounts of Ni. Coffee growth decreased upon adding Ni to the solution culture at rates of 0.0, 0.5, and 1.0 mg/1. The thermodynamic analysis of the nutrient solution predicts no solid phases under the conditions of the experiment and the most predominant species of Ni in solution was bound with EDTA. Such ionic form of Ni in the nutritive solution is supposed to be correlated with its absorption and translocation by the roots of the coffee tree. Leaf Ni concentration of 30 to 40 and 70 to 80 μg Ni/g were associated with medium and very severe leaf toxicity symptoms respectively. Nickel toxicity symptons include chlorosis and necrotic spots on younger leaves and internodes; leaves fall prematurely, dieback, and streak necrosis of the leaves, petioles and branches. Excess of Ni in solution increased leaf Mn, Fe, and Zn, decreased leaf Ca, but did not affect leaf Mg and total N. It seems reasonable to speculate that the Ni caused root damage which facilitated Mn, Fe, and Zn uptake. Total leaf chlorophyll decreased as leaf Ni increased. The regression equation for total leaf chlorophyll (Y = mg/g) as related to leaf Ni (μg Ni/g) was: Y= 2.10-0.006 (leaf Ni). It was found that any value of chlorophyll content in the third pair of coffee leaves below 2 mg/g of fresh tissue was associated with leaf chlorosis.