Mineral nutrition of Norway spruce (Picea abies (L.) Karst.) and beech (Fagus sylvatica L.) was investigated along a transect extending from northern Sweden to central Italy. Nitrogen (N) concentrations of needles and leaves in stands growing on acid soils did not differ significantly between central Italy and southern Sweden (1.0 ± 0.1 mmol N g−1 for needles and 1.9 ± 0.14 mmol N g−1 for leaves). In both species, foliar N concentrations were highest in Germany (1.2 mmol N g−1 for needles and 2.0 mmol N g−1 for leaves) and decreased by 50% toward northern Sweden (0.5 mmol N g−1). Both species showed constant S/N and P/N ratios along the transect. Calcium, K and Mg concentrations generally reflected local soil conditions; however, Mg concentrations reached deficiency values in Germany. Leaf area per unit dry weight varied significantly along the transect with lowest values for Norway spruce recorded in northern Sweden and Italy (3.4 m2 kg−1) and a maximum in central Europe (4.7 m2 kg−1). A similar pattern was observed for beech.
Despite the low variation in foliar N concentrations on the large geographic scale, local and regional variations in N concentrations equalled or exceeded the variation along the entire continental transect. Furthermore, nutrient contents (i.e., nutrient concentration × dry weight per needle or leaf) showed a greater variation than nutrient concentrations along the transect. Nitrogen contents of Norway spruce needles reached minimum values in northern Sweden (2.4 μmol N needle−1) and maximum values in Denmark (5.0 μmol N needle−1). The N content of beech leaves was highest in Denmark (242 μmol N leaf−1).
At the German site, foliar N content rather than N concentration reflected the seasonal dynamics of foliar growth and N storage of the two species. During foliage expansion, there was an initial rapid increase in N content and a decrease in N concentration. This pattern lasted for about 2 weeks after bud break and was followed by 6 weeks during which dry weight and N content of the foliage increased, resulting in a further decrease in N concentration. During summer, dry weight and N content of mature needles of Norway spruce increased further to reach a maximum in autumn, whereas N concentration remained constant. In spring, reallocation of N from 1- and 2-year-old needles was 1.5 and 1.0 μmol N needle−1, respectively. This remobilized N was a major source of N for the development of new needles, which had an N content of 1.5 μmol N needle−1 after bud break. The seasonal remobilization of N from old foliage decreased with increasing needle age. Needle N content and dry weight decreased progressively with age (1 μmol N needle−1 between age classes 2 and 5), whereas N concentrations remained constant.
For Norway spruce, annual stemwood production was correlated with needle N content but not with foliar N concentration or with the total amount of N in the canopy. Interspecific and geographical differences in plant nutrition are discussed on the basis of competitive demands for C and N between growth of foliage and wood.