Effects of Cd and Zn on the development of annual xylem rings of young Norway spruce (Picea abies) plants

Abstract

Three-year-old spruce (Picea abies) saplings were planted and cultivated for 2 years in pots with 3 1 substrate, consisting of a homogenized mixture of sand, peat and forest soil with a high organic content (volume ratio 1∶1.5∶2). This substrate was amended with 10–180 μmol Cd [kg soil dry weight (DW)]−1, 50–7500 μmol Zn (kg soil DW)−1 (determined with 1 M ammonium acetate extracts) or combinations of both elements. Annual xylem growth rings in stems of plants treated with 50 μmol Cd (kg soil DW)−1 or 7500 μmol Zn (kg soil DW)−1 were significantly narrower than in control plants. Growth reductions were more pronounced in the second year of the experiment. The contents of Cd and Zn in stem wood and needles were positively correlated with the substrate concentrations. The Mg contents of the spruce needles were inversely correlated with soil concentrations of Cd and Zn. Root development was impeded at moderate concentrations of Cd (50 μmol kg−1) or Zn (1000 μmol kg−1) in the substrate. The adverse effects of potentially toxic trace elements, like Cd or Zn, on xylem growth of spruce plants are discussed with regard to possible growth reductions in forest trees under field conditions.