• trees;
  • NHequation image;
  • NOequation image;
  • specific N-uptake rates;
  • accumulation rates of amino acids;
  • mineral soil


Species-specific uptake and allocation mechanisms for N are scarce, in particular when trees are cultivated in potted soil under more natural conditions than in hydroponic culture. The objective of this study was to compare specific N-uptake rates for economically and ecologically important tree species in Central European forests: pine (Pinus sylvestris), spruce (Picea abies), oak (Quercus petraea), beech (Fagus sylvatica), lime (Tilia cordata), and ash (Fraxinus excelsior) when they grow in mineral soil from an old fallow site with a pH of 6. We used an 15N-labeling method to measure tree seedling 15N uptake in potted soils (Humic Cambisol) when both N forms NHequation image and NOequation image were simultaneously present in the soil solution for interspecies comparison and assessment of relationships between specific 15N-uptake rates and amino acid–accumulation rates or relative growth rates (RGR). The results demonstrate that tree species varied significantly in their capacity to take up NHequation image or NOequation image into roots, stems, or leaves, but indicate only marginal differences in their preference for NHequation image or NOequation image when they grow in mineral soil. The ranking of specific 15N-uptake rates for NHequation image and NOequation image was oak < beech < spruce < pine < lime < ash. Fine roots of all species had the highest specific 15N-uptake rates for both N forms, followed by total roots, leaves/needles, and stems. As regards tree seedling species, we found negative relationships between glutamine (Gln)-accumulation rates in leaves/needles and total 15N-uptake rates in fine roots. Noteworthy was the fact that, at high Gln-accumulation rates, the N-uptake system in fine roots of ash was probably lower under feedback inhibition by the amino acid.