Sources of nitrous oxide emitted from European forest soils

Abstract

Abstract. Forest ecosystems may provide strong sources of nitrous oxide (N 2 O), which is important for atmospheric chemical and radiative properties. Nonetheless, our understanding of controls on forest N 2 O emissions is insufficient to narrow current flux estimates, which still are associated with great uncertainties. In this study, we have investigated the quantitative and qualitative relationships between N-cycling and N 2 O production in European forests in order to evaluate the importance of nitrification and denitrification for N 2 O production. Soil samples were collected in 11 different sites characterized by variable climatic regimes and forest types. Soil N-cycling and associated production of N 2 O was assessed following application of 15 N-labeled nitrogen. The N 2 O emission varied significantly among the different forest soils, and was inversely correlated to the soil C:N ratio. The N 2 O emissions were significantly higher from the deciduous soils (13 ng N 2 O-N cm −3 d −1 ) than from the coniferous soils (4 ng N 2 O-N cm −3 d −1 ). Nitrate (NO − 3 ) was the dominant substrate for N 2 O with an average contribution of 62% and exceeding 50% at least once for all sites. The average contribution of ammonium (NH + 4 ) to N 2 O averaged 34%. The N 2 O emissions were correlated with gross nitrification activities, and as for N 2 O, gross nitrification was also higher in deciduous soils (3.4 µg N cm −3 d −1 ) than in coniferous soils (1.1 µg N cm −3 d −1 ). The ratio between N 2 O production and gross nitrification averaged 0.67% (deciduous) and 0.44% (coniferous). Our study suggests that changes in forest composition in response to land use activities and global change may have implications for regional budgets of greenhouse gases. From the study it also became clear that N 2 O emissions were driven by the nitrification activity, although the N 2 O was produced per se mainly from denitrification. Increased nitrification in response to accelerated N inputs predicted for forest ecosystems in Europe may thus lead to increased greenhouse gas emissions from forest ecosystems.

The importance of denitrification for N2O emissions from an N-saturated forest in SW China: results from in situ 15N labeling experiments

“…It appeared that nitrification contributed very little to N 2 O production within the observed WFPS range. This was in contrast to several other studies (Bateman and Baggs 2005;Mathieu et al 2006;Zhang et al 2011a;Khalil et al 2004;Ambus et al 2006;Mørkved et al 2006;Russow et al 1994;Wolf and Brumme 2002;Wolf and Russow 2000;Eickenscheidt et al 2011) who found that significant contributions of nitrification to N 2 O production occurred at intermediate WFPS ranges whereas denitrification generally occurred at high soil moisture content. Comparing soil types in the above cited studies, it appears that also soil pH could be an important factor for N 2 O source partitioning, as it interacts with the soil moisture relationship; in neutral to alkaline soils the contribution of nitrification to N 2 O emission seems to be high and less sensitive to WFPS than the contribution of denitrification (Khalil et al 2004;Mathieu et al 2006;Bateman and Baggs 2005).…”

“…However, the contribution of nitrification was not addressed in this study. In a laboratory incubation experiment with acidic soils from 11 different forest sites across Europe, Ambus et al (2006) found that NO 3 -contributed on average 62 % to N 2 O production while NH 4…”

Effects of nitrogen deposition and fertilization on N transformations in forest soils: a review

“…Correspondingly, different approaches and techniques, including inhibition of low concentration of acetylene on nitrification, 15 N trace methods, natural abundance of 15 N in N 2 O, and 15 N tracing model, are applied to identify the pathways and rates of soil N 2 O production, which have been well summarized by Müller et al (2014) and Kulkarni et al(2014). For example, Ambus et al (2006) found the main source of N 2 O emitted from temperate European forests characterized by various climatic regimes and forest types (seven coniferous sites and four deciduous sites) is nitrification following the application of laboratory 15 N labeling of intact soil cores and linear mixing model. Furthermore, a low-concentration 15 N-labeled ammonium-nitrate solution was applied to a temperate beech and spruce forest to simulate N deposition and thus to assess the direct contribution of N deposition to N 2 O emissions in temperate forests, with the results showing that stimulated N loss as N 2 O was mainly driven by denitrification (Eickenscheidt et al 2011).…”

Impact of the size of nitrogen fertiliser application rate on N₂O flux

“…Nitrous oxide (N 2 O) is among the most important greenhouse gases, contributing by 6% to global warming (Loubet et al 2011;Ranucci et al 2011), and directly affects the stratospheric ozone layer (Willianms et al 1992;Ravishankara et al 2009). Nitrous oxide emitted from soils leads to N loss from the ecosystem and is produced by nitrification and denitrification microbiological activities (Skiba et al 1993;Ambus et al 2006;Jiang-Gang et al 2007;Senbayram et al 2012) and chemodenitrification at low pH (< 5.5) (Van Cleemput, Samater 1996). The major N 2 O source is denitrification (Skiba et al 1997;Skiba, Smith 2000;Ruser et al 2001).…”