Nitrous oxide emissions from a peatbog after thirteen years of experimental nitrogen deposition

Other literature type English OPEN
Leeson, Sarah R. ; Levy, Peter E. ; Dijk, Netty ; Drewer, Julia ; Robinson, Sophie ; Jones, Matthew R. ; Kentisbeer, John ; Washbourne, Ian ; Sutton, Mark A. ; Sheppard, Lucy J. (2016)

Nitrogen deposition was experimentally increased on a Scottish peat bog over a period of thirteen years (2002&ndash;2015). Nitrogen was applied in three forms, NH<sub>3</sub> gas, NH<sub>4</sub><sup>+</sup> solution, and NO<sub>3</sub><sup>&minus;</sup> solution, at rates ranging from ambient (8) to 64 kg N ha<sup>&minus;1</sup> y<sup>&minus;1</sup>, and higher near the NH<sub>3</sub> fumigation source. An automated system was used to apply the nitrogen, such that the deposition was realistic in terms of rates and high frequency of deposition events. We measured the response of nitrous oxide (N<sub>2</sub>O) flux to the increased nitrogen input. Prior expectations, based on the IPCC default emission factor, were that 1 % of the added nitrogen would be emitted as N<sub>2</sub>O. In the plots treated with NH<sub>4</sub><sup>+</sup> and NO<sub>3</sub><sup>&minus;</sup> solution, no response was seen, and there was a tendency for N<sub>2</sub>O fluxes to be reduced by additional nitrogen, though this was not significant. Areas subjected to high NH<sub>3</sub> emitted more N<sub>2</sub>O than expected, up to 8.5 % of the added nitrogen. Differences in the response are related to the impact of the nitrogen treatments on the vegetation. In the NH<sub>4</sub><sup>+</sup> and NO<sub>3</sub><sup>&minus;</sup> treatments, all the additional nitrogen is effectively immobilised in the vegetation and top 10 cm of peat. In the NH<sub>3</sub> treatment, much of the vegetation was killed off by high doses of NH<sub>3</sub>, and the nitrogen was presumably more available to denitrifying bacteria. The design of the wet and dry experimental treatments meant that they differed in statistical power, and we are less likely to detect an effect of the the NH<sub>4</sub><sup>+</sup> and NO<sub>3</sub><sup>&minus;</sup> treatments, though they avoid issues of pseudo-replication.
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