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Application of ammonium nitrate (NH4NO3) to cores of Sphagnum magellanicum in situ at 2-week intervals for 20 weeks from mid-June at a raised mire in north-east Scotland stimulated growth at only 1 g N m−2 year−1, whereas greater additions, equivalent to 3 and 10g N m−2, had no significant effect. The N concentration of the moss tissues increased linearly with increasing levels of NH4NO3 up to 10g N m−2 year−1. In cores receiving an additional of 10g N m−2 year−1, there was a significant increase in the concentration of organic N extracted from the moss in the surface 5 cm with 0.5 M K2SO4. The concentration of organic N correlated linearly with the quantity of N applied. NH4NO3 significantly reduced the rate of CO2 evolved from samples from a depth of 5–10 cm, and increased microbial C as measured by the substrate-induced respiration (SIR) method. Overall, inorganic N additions at 1 g N m−2 year−1 reduced the specific rate of respiration and activity of the microbial biomass at this depth. The mean total N:P ratios for the profile ranged from 24 to 28, suggesting that the site was P-deficient, which probably limited the growth response of S. magellanicum. [ABSTRACT FROM AUTHOR]