Factors controlling regional differences in forest soil emission of nitrogen oxides (NO and N<sub>2</sub>O)

Abstract

Abstract. Soil emissions of NO and N 2 O were measured continuously at high frequency for more than one year at 15 European forest sites as part of the EU-funded project NOFRETETE. The locations represent different forest types (coniferous/deciduous) and different nitrogen loads. Geographically they range from Finland in the north to Italy in the south and from Hungary in the east to Scotland in the west.The highest NO emissions were observed from coniferous forests, whereas the lowest NO emissions were observed from deciduous forests. The NO emissions from coniferous forests were highly correlated with N-deposition. The site with the highest average annual emission (82 µg NO-N m −2 h −1 ) was a spruce forest in South-Germany (Höglwald) receiving an annual N-deposition of 2.9 g m −2 . NO emissions close to the detection limit were observed from a pine forest in Finland where the N-deposition was 0.2 g N m −2 a −1 . No significant correlation between N 2 O emission and N-deposition was found. The highest average annual N 2 O emission (20 µg N 2 O-N m −2 h −1 ) was found in an oak forest in the Mátra mountains (Hungary) receiving an annual N-deposition of 1.6 g m −2 . N 2 O emission was significantly negatively correlated with the C/N ratio.The difference in N-oxide emissions from soils of coniferous and deciduous forests may partly be explained by differences in N-deposition rates and partly by differences in characteristics of the litter layer and soil. NO was mainlyCorrespondence to: K. Pilegaard (kim.pilegaard@risoe.dk) derived from nitrification whereas N 2 O was mainly derived from denitrification. In general, soil moisture is lower at coniferous sites (at least during spring time) and the litter layer of coniferous forests is thick and well aerated favouring nitrification and thus release of NO. Conversely, the higher rates of denitrification in deciduous forests due to a compact and moist litter layer lead to N 2 O production and NO consumption in the soil.The two factors soil moisture and soil temperature are often explaining most of the temporal variation within a site. When comparing annual emissions on a regional scale, however, factors such as nitrogen deposition and forest and soil type become much more important.

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

“…However, more and more attention is being paid to denitrification process in forests under increasing N deposition due to the high global warming potential of N 2 O (Hall and Matson 1999;Levy-Booth et al 2014). Although some studies have shown that N deposition and fertilization to forest ecosystems have minor effects on soil N 2 O emission (Magill et al 1997), there is mounting evidence that excessive N deposition to forest ecosystems, especially to N-unlimited forest ecosystems, has promoted soil N 2 O emission (Butterbach-Bahl et al 1998;Gundersen et al 2012;Hall and Matson 1999;Jassal et al 2011;Pilegaard et al 2006;Zhang et al 2008). For example, Hall and Matson (1999) found that N addition stimulated N 2 O emissions in both phosphorus (P)-limited and N-limited tropical forest soils, with a greater stimulation in the P-limited forest.…”

“…Also, estimated N loss as NO could reach up to 24.5-34.5 % of N deposited or added to forests (Butterbach-Bahl et al 2002;Pilegaard et al 2006). Furthermore, it has been reported that the main source for NO in forest soils is nitrification (autotrophic nitrification) (Pilegaard et al 2006;Venterea et al 2003), and the key factors regulating its emission could be soil moisture, soil temperature, litter layer properties (e.g., water content and thickness), N deposition (at least for European coniferous forests), and soil pH (Pilegaard et al 2006;Venterea et al 2003).…”

“…However, NO is another important N loss species from forest soils (Butterbach-Bahl et al 2002;Hall and Matson 1999;Horváth et al 2006;Pilegaard et al 2006;Venterea et al 2003), and in some cases, the NO emission rate is even larger than N 2 O emission rate in N-deposited and N-fertilized forest sites (Butterbach-Bahl et al 2002;Pilegaard et al 2006;Venterea et al 2003). As summarized in Table 3, NO emission rates from European coniferous forests are highly correlated with N deposition, with the highest average annual emission rate up to 81.7 μg NO-N m −2 h −1 (Pilegaard et al 2006). Also, estimated N loss as NO could reach up to 24.5-34.5 % of N deposited or added to forests (Butterbach-Bahl et al 2002;Pilegaard et al 2006).…”

“…At site level, the denitrifier community activity and denitrification processes may be greatly influenced by soil moisture and O 2 partial pressure (Gundersen et al 2012;Pilegaard et al 2006;Russow et al 2009), organic C and soil pH (Bárta et al 2010;Gundersen et al 2012;Levy-Booth et al 2014;Pilegaard et al 2006), and oxidation capacity (OXC) (Zhang et al 2009). In addition, the accessibility of NO 3 − ions to denitrifiers on soil particles can also exert an influence on denitrification (Bengtsson and Bergwall 2000).…”

Nitrogen balance of a boreal Scots pine forest

“…Anthropogenic emissions of reactive nitrogen (N) have markedly increased the atmospheric N deposition to forests, especially around industrialized regions (Pinho et al, 2012;Gruber and Galloway, 2008;Galloway et al, 2003). There is, however, a large spatial variability in the effects by N deposition (Magnani et al, 2007;Fischer et al, 2010).…”