Denitrification triggered by nitrogen addition in Sphagnum magellanicum peat

Ombrotrophic (rain-fed) Sphagnum-mires do not significantly contribute to gaseous nitrogen (N) emissions to the atmosphere. However, increasing levels of N deposition reduce Sphagnum growth and moss cover. As a consequence, higher amounts of mineral N reach the underlying peat beneath the moss layer. The aim of our work was to determine the effects of supplementary N inputs to peat beneath Sphagnum magellanicum carpets. Peat cores were incubated in controlled laboratory conditions of temperature and humidity, and the impact of increasing N inputs was evaluated on denitrification rates, basal respiration and methane emissions. Rates of denitrification were quickly stimulated by addition of 1 g N m−2 but rates were not significantly elevated in the short-term (9 days) by further additions of up to 10 g N m−2. Over a longer term period (up to 45 days), denitrification rates followed an exponential (10 g N m−2 addition) or a gamma (1 g N m−2) function. Findings from this study support the hypothesis that mineral-N addition in atmospheric deposition will have a negative effect on peat biogeochemistry, by modifying its N sink capacity via denitrification leading to a potential increase in N2O emissions.