Environmental Pollution (Series A) 38 (1985) 375-381 Effect of Zinc, Cadmium and Mercury on Root Elongation of Picea abies (Karst.) Seedlings, and the Significance of These Metals to Forest Die-Back D. L. Godbold & A. Hiittermann Forstbotanisches Institute, Universit/it G6ttingen, Biisgenweg 2, 3400 G6ttingen, Federal Republic of Germany. ABSTRACT Inhibition of root elongation was used to assess the toxicity of Zn, Cd and Hg to Picea abies seedlings. The order of toxicity was found to be Hg > Cd > Zn. A comparison of the levels of these metals, shown to inhibit root elongation in nutrient solution, with those in forest soils under stands showing symptoms of die-back, suggests that metal levels in such • soils are sufficiently high to influence root growth. INTRODUCTION The current die-back occurring in forests in the Federal Republic of Germany has been attributed mainly to the effect of acid deposition produced by atmospheric pollution. Associated with trees showing the symptoms of die-back are high heavy metal contents in both roots and aerial parts (Mayer & Heinrichs, 1981; Mayer, 1983). Similarly, Mayer (1981) has shown that the metals Cr, Fe, Co, Ni, Zn, Cu, Cd and Pb accumulate in the humus layer of soils under tree stands showing die-back. This soil layer has been shown to be an important area for root growth of spruce Picea abies (Ulrich, 1983). However, it is not known whether the levels of heavy metals found in this soil layer and the trees themselves are sufficiently high to contribute to the decline of the trees. Inhibition of root elongation has been shown to be a sensitive parameter for assessing the toxicity of heavy metals (Hassett et al., 1976; 375 Environ. Pollut. Ser. A. 0143-1471/85/$03.30 © Elsevier Applied Science Publishers Ltd, England, 1985. Printed in Great Britain