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

• Main Authors: P. Levy, C. Field, N. van Dijk, S. R. Leeson, I. D. Leith, L. J. Sheppard
• Format: Article
• Language: English
• Published: Copernicus Publications 2013-01-01
• Series: Biogeosciences
• Online Access: http://www.biogeosciences.net/10/149/2013/bg-10-149-2013.pdf

Peatlands represent a vast carbon reserve that has accumulated under conditions of low nitrogen availability. Given the strong coupling between the carbon and nitrogen cycles, we need to establish the consequences of the increase in reactive nitrogen deposition for the sustainability of peatlands, and whether the form in which the nitrogen is deposited makes a difference. We have addressed these questions using a globally unique field simulation of reactive N deposition as dry deposited ammonia and wet deposited reduced N, ammonium and oxidised N, nitrate, added as ammonium chloride or sodium nitrate, to an ombrotrophic peatland, Whim bog in SE Scotland. Here we report the fate of 56 kg N ha⁻¹ yr⁻¹ additions over 10 yr and the consequences. The effects of 10 yr of reactive N additions depended on the form in which the N was applied. Ammonia-N deposition caused the keystone <i>Sphagnum</i> species, together with the main shrub <i>Calluna</i> and the pleurocarpous mosses, to disappear, exposing up to 30% of the peat surface. This led to a significant increase in soil water nitrate and nitrous oxide emissions. By contrast wet deposited N, despite significantly reducing the cover of <i>Sphagnum</i> and <i>Pleurozium</i> moss, did not have a detrimental effect on <i>Calluna</i> cover nor did it significantly change soil water N concentrations or nitrous oxide emissions. Importantly 10 yr of wet deposited N did not bare the peat surface nor significantly disrupt the vegetation enabling the N to be retained within the carbon rich peatland ecosystems. However, given the significant role of <i>Sphagnum</i> in maintaining conditions that retard decomposition, this study suggests that all nitrogen forms will eventually compromise carbon sequestration by peatlands through loss of some keystone <i>Sphagnum</i> species.