%0 Articles
%T Nitrous oxide emissions from selected natural and managed northern ecosystems
%A Pihlatie, Mari
%D 2007
%J Dissertationes Forestales
%V 2007
%N 36
%R doi:10.14214/df.36
%U http://dissertationesforestales.fi/article/1818
%X Microbial activity in soils is the main source of nitrous oxide (N<sub>2</sub>O) to the atmosphere. Nitrous oxide is a strong greenhouse gas in the troposphere and participates in ozone destructive reactions in the stratosphere. The constant increase in the atmospheric concentration, as well as uncertainties in the known sources and sinks of N<sub>2</sub>O underline the need to better understand the processes and pathways of N<sub>2</sub>O in terrestrial ecosystems. This study aimed at quantifying N<sub>2</sub>O emissions from soils in northern Europe and at investigating the processes and pathways of N<sub>2</sub>O from agricultural and forest ecosystems. Emissions were measured in forest ecosystems, agricultural soils and a landfill, using the soil gradient, chamber and eddy covariance methods. Processes responsible for N<sub>2</sub>O production, and the pathways of N<sub>2</sub>O from the soil to the atmosphere, were studied in the laboratory and in the field. These ecosystems were chosen for their potential importance to the national and global budget of N<sub>2</sub>O.
Laboratory experiments with boreal agricultural soils revealed that N<sub>2</sub>O production increases drastically with soil moisture content, and that the contribution of the nitrification and denitrification processes to N<sub>2</sub>O emissions depends on soil type. Laboratory study with beech (Fagus sylvatica) seedlings demonstrated that trees can serve as conduits for N<sub>2</sub>O from the soil to the atmosphere. If this mechanism is important in forest ecosystems, the current emission estimates from forest soils may underestimate the total N<sub>2</sub>O emissions from forest ecosystems. Further field and laboratory studies are needed to evaluate the importance of this mechanism in forest ecosystems. The emissions of N<sub>2</sub>O from northern forest ecosystems and a municipal landfill were highly variable in time and space. The emissions of N<sub>2</sub>O from boreal upland forest soil were among the smallest reported in the world. Despite the low emission rates, the soil gradient method revealed a clear seasonal variation in N<sub>2</sub>O production. The organic topsoil was responsible for most of the N<sub>2</sub>O production and consumption in this forest soil. Emissions from the municipal landfill were one to two orders of magnitude higher than those from agricultural soils, which are the most important source of N<sub>2</sub>O to the atmosphere. Due to their small areal coverage, landfills only contribute minimally to national N<sub>2</sub>O emissions in Finland. The eddy covariance technique was demonstrated to be useful for measuring ecosystem-scale emissions of N<sub>2</sub>O in forest and landfill ecosystems. Overall, more measurements and integration between different measurement techniques are needed to capture the large variability in N<sub>2</sub>O emissions from natural and managed northern ecosystems.