Toxicity of metals in plants. I. Characterization of manganese toxicity in coffee

Abstract

Coffee seedlings (Coffea arabica L.) cv. "Catuaí vermelho” were grown in sand culture with different amounts of Mn. The objective was to determine and characterize toxicities of this metal. Mn uptake was proportional to the supply and plant injuries were proportional to Mn uptake. The regression equation for leaf Mn (Y = µ g Mn/g) as related to solution Mn (mg Mn/l) was: Y = 352.59 + 132.59 (sol. Mn) (R = 0.965***). Twenty-five percent of the yield decrement was associated with solution Mn of 20 mg Mn/l or leaf Mn ranged from 2,500 to 2,800 µg Mn/g. The regression equation for plant dry weight (Y = g/plants) as related to leaf Mn (µg Mn/g) was: Y = 213.41 - 0.022 (leaf Mn) (R = 0.613*). Maximum yields were associated with Mn/Fe ratio in leaf tissue of 7.64 and decrease to 25% to the maximum as this ratio was increased to 18. Excess of Mn in solution decreased leaf Fe and Ca but did not affect leaf B, Zn, Mg and total N. Total leaf chlorophyll increased to a maximum concentration of 2.6 mg/g fresh tissue when leaf Mn was 608 µg/g and steadily decreased to 1.85 mg/g as the leaf Mn was increased to 2,580 µg/g. Leaf Mn concentrations of 1,200 and 2,600 µg Mn/g were associated with medium and very severe leaf toxicity symptoms respectively. Manganese toxicity symptoms were marginal chlorosis and few necrotic spots on younger leaves.