Effect of varied soil nitrogen supply on growth and nutrient uptake of young Norway spruce plants grown in a shaded environment

To understand the effect of increased soil N supply on tree growth and nutr ient uptake, three-year-old Norway spruce seedlings were gown in pots on lo w-nutrient mineral forest soil supplemented with N in mineral or organic fo rm. Outdoor shaded growth conditions were used, to test the hypothesis that shaded plants are particularly susceptible to high soil N supply. Plants w ere harvested eleven months after planting. Shoot growth was not affected b y the N supply, but N concentrations in needles and roots were increased in plants supplied with mineral N (150 or 300 mg N Fg soil](-1)). Root growth was drastically reduced and root/shoot ratios were decreased in plants wit h higher N uptake. A high supply of mineral N to soil also decreased the co ncentrations of other essential elements (P, K) in the needles and thus had effects on plant growth which may impair the stress resistance of trees. O rganic N in the form of keratin (150 mg N Fg soil](-1)) did not influence p lant growth significantly. The adverse effects of high mineral N supply wer e particularly pronounced under shaded conditions in comparison to results from other experiments using higher light intensity and temperature conditi ons.