Consistent patterns of foliar N concentration and δ¹⁵N were found in age sequences of foliage. N concentration decreased with age and δ¹⁵N increased with age. Patterns of δ¹⁵N may be useful in studying nutrient retranslocation within the canopy because, as far as it is known, they are unaffected by contemporary changes in other leaf components. No evidence for increased efficiency of N recycling in spruce from mixed stands as compared to spruce from pure stands was found. The δ¹⁵N data appear to confirm that the amount of N retranslocated depends on the N concentration of the foliage. There was evidence that in a young site the δ¹⁵N value of externally available N in the mixed stands became increasingly enriched over time, while the δ¹⁵N value of externally available N in the mixed stands at a mature site remained constant. Foliar N concentrations and δ¹⁵N of spruce in mixtures with different nurse species and in different ratios were measured. The δ¹⁵N values of nurse foliage differed significantly between species, but no significant effects of nurse species on δ¹⁵N value of the spruce were found. Increasing the proportion of the nurse in a stand increased the foliar N concentration of spruce and caused an enrichment in the ¹⁵N abundance. Soils from one site were subjected to a series of extractions to extract N pools of different liability. N concentrations of 4 pools were measured and δ¹⁵Nvalues calculated. Total soil N in mixed stands was enriched in δ¹⁵N relative to pure stands. It was not possible to identify the pools available to spruce in pure and mixed stands because of large errors in δ¹⁵N values. Organic N pools were consistently enriched relative to largely inorganic N pools. The foliar δ¹⁵N values of spruce in pure stands were close to those of the hot K₂SO₄ extractable pool containing microbial N and amino acids, whereas in the mixed stands, the foliar δ¹⁵N values of both spruce and pine were close to those of the hot HCI extractable pool containing less labile organic N. The results are discussed in relation to the mixtures effect. It is concluded that patterns of ¹⁵N natural abundance in pure and mixed stands of spruce support the hypothesis that in mixtures, spruce has access to a source of organic N not normally available to it in pure stands.