EFFECTS OF CD AND ZN ON THE DEVELOPMENT OF ANNUAL XYLEM RINGS OF YOUNG NORWAY SPRUCE (PICEA-ABIES) PLANTS

Three-year-old spruce (Picea abies) saplings were planted and cultivat ed 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 (vo lume ratio 1: 1.5: 2). This substrate was amended with 10-180 mumol Cd [kg soil dry weight (DW)]-1, 50-7500 mumol Zn (kg soil DW)-l (determi ned with 1 M ammonium acetate extracts) or combinations of both elemen ts. Annual xylem growth rings in stems of plants treated with 50 mumol Cd (kg soil DW)-1 or 7500 mumol Zn (kg soil DW)-1 were significantly narrower than in control plants. Growth reductions were more pronounce d in the second year of the experiment. The contents of Cd and Zn in s tem wood and needles were positively correlated with the substrate con centrations. The Mg contents of the spruce needles were inversely corr elated with soil concentrations of Cd and Zn. Root development was imp eded at moderate concentrations of Cd (50 mumol kg-1) or Zn (1000 mumo l kg-1) in the substrate. The adverse effects of potentially toxic tra ce elements, like Cd or Zn, on xylem growth of spruce plants are discu ssed with regard to possible growth reductions in forest trees under f ield conditions.