Structural observations on needles exposed to elevated levels of copper and nickel

The two youngest needle age classes from 4–5 pines were collected in September 1995 for microscopy at Kevo, norther Finland. During the years 1991–1995, 461 mg/m2 sulphate had been applied in irrigated control (IC) tests and 519 mg/m2 sulphate, 69 mg/m2 copper and 43 mg/m2 nickel in metal treatment (Cu/Ni). The mean pH of the solution was 6.0 in IC treatment and 5.7 in Cu/Ni treatment. Metals had not altered the needle structure significantly, but a retarded hardening process was observed. Summer frost type symptoms were common in unwatered control needles.