Factors controlling regional differences in forest soil emission of nitrogen oxides (NO and N2O)
Other literature type
Pihlatie, M. K.
(issn: 1726-4189, eissn: 1726-4189)
Soil emissions of NO and N<sub>2</sub>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<sup>−2</sup> h<sup>−1</sup>) was a spruce
forest in South-Germany (Höglwald) receiving an annual N-deposition of 2.9 g m<sup>−2</sup>.
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<sup>−2</sup> a<sup>−1</sup>. No
significant correlation between N<sub>2</sub>O emission and N-deposition was found. The
highest average annual N<sub>2</sub>O emission (20 μg N<sub>2</sub>O-N m<sup>−2</sup> h<sup>−1</sup>)
was found in an oak forest in the Mátra mountains (Hungary) receiving an
annual N-deposition of 1.6 g m<sup>−2</sup>. N<sub>2</sub>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 mainly
derived from nitrification whereas N<sub>2</sub>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<sub>2</sub>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.