LONG-TERM EFFECTS OF A HIGH-NITROGEN SUPPLY TO SOIL ON THE GROWTH ANDNUTRITIONAL-STATUS OF YOUNG NORWAY SPRUCE TREES

Central European forests are characterised by increasing N inputs. In a pot experiment with 3-year-old trees, the effects of varied N supply in soil (in mineral or organic form) on the growth and nutrient uptak e of Norway spruce were examined over a period of 20 months. A nutrien t-poor mineral forest soil was used in the experiment. N was added to the soil once, at the onset of the experiment. High mineral N supply ( NH4NO3) decreased root growth and the root/shoot ratio of newly grown plant biomass, which resulted in wide N/P and N/K ratios in needles, a nd significantly decreased needle K concentrations. On the contrary, n eedle Ca concentrations were increased in plants with additional miner al N supply. The organic N form (keratin) slowly became available to p lants, and also decreased the root/shoot ratio. In contrast to many ob servations in short-term experiments, the specific root length and the number of root tips per cm of root length were not affected by the so il N supply. High supply of mineral N did not cause visual symptoms of toxicity or damage in the plant. Induced cation or P deficiency may b e a harmful consequence of high soil N levels, but will occur only whe n the soil supply of these nutrients is critically low. (C) 1998 Elsev ier Science Ltd. All rights reserved.