Nutrient and microbial changes in the peat profile beneath Sphagnum magellanicum in response to additions of ammonium nitrate.
Abstract
Applications of ammonium nitrate (NH4NO3) to cores of Sphagnum magellanicumin 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/m2 per year, whereas greater additions, equivalent to 3 and 10 g N/m2, had no significant effect. The N concentration of the moss tissues increased linearly with increasing levels of NH4NO3 up to 10 g N/m2 per year. In cores receiving an addition of 10 g N/ m2 per year, there was a significant increase in the concentration of organic N extracted from the moss in the surface 5 cm with 0.5 smallcap˜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/m2 per year 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 limited the growth response of S. magellanicum.