Fate of N in a peatland, Whim bog: immobilisation in the vegetation and peat, leakage into pore water and losses as N2O depend on the form of N

[摘要] Peatlands represent a vast carbon reserve that has accumulated underconditions of low nitrogen availability. Given the strong coupling betweenthe carbon and nitrogen cycles, we need to establish the consequences of theincrease in reactive nitrogen deposition for the sustainability ofpeatlands, and whether the form in which the nitrogen is deposited makes adifference. We have addressed these questions using a globally unique fieldsimulation of reactive N deposition as dry deposited ammonia and wetdeposited reduced N, ammonium and oxidised N, nitrate, added as ammoniumchloride or sodium nitrate, to an ombrotrophic peatland, Whim bog in SEScotland. Here we report the fate of 56 kg N ha⁻¹ yr⁻¹ additionsover 10 yr and the consequences. The effects of 10 yr of reactive Nadditions depended on the form in which the N was applied. Ammonia-Ndeposition caused the keystone Sphagnum species, together with the main shrubCalluna and the pleurocarpous mosses, to disappear, exposing up to 30% of thepeat surface. This led to a significant increase in soil water nitrate andnitrous oxide emissions. By contrast wet deposited N, despite significantlyreducing the cover of Sphagnum and Pleurozium moss, did not have a detrimental effect onCalluna cover nor did it significantly change soil water N concentrations ornitrous oxide emissions. Importantly 10 yr of wet deposited N did notbare the peat surface nor significantly disrupt the vegetation enabling theN to be retained within the carbon rich peatland ecosystems. However, giventhe significant role of Sphagnum in maintaining conditions that retarddecomposition, this study suggests that all nitrogen forms will eventually compromisecarbon sequestration by peatlands through loss of some keystone Sphagnum species.

[学科分类] 地球化学与岩石