Atmospheric impact of nitrous oxide uptake by boreal forest soils can be comparable to that of methane uptake
Henri Siljanen, Nina Welti, Carolina Voigt, Juha Heiskanen, Christina Biasi, Pertti J. Martikainen
Abstract
Abstract Aims Environmental factors controlling nitrous oxide (N 2 O) uptake in forest soils are poorly known, and the atmospheric impact of the forest N 2 O sink is not well constrained compared to that of methane (CH 4 ). Methods We compared nitrous oxide (N 2 O) and CH 4 fluxes over two growing seasons in boreal forest soils located in Eastern Finland. Within a spruce forest, we compared plots with long-term nitrogen (N) fertilization history and non-fertilized plots, and additionally pine forest plots without a fertilization history. The flux data was complemented with measurements of climatic conditions and soil physical and chemical characteristics, in order to identify factors affecting N 2 O and CH 4 fluxes. Results Non-fertilized spruce forest soils showed the highest cumulative N 2 O uptake among the sites, whereas the pine forest site displayed low cumulative N 2 O emission. Nitrous oxide uptake was favored by high soil silt and water content. The low temperature seasons, spring and autumn, had the highest N 2 O uptake, likely associated with high soil water content typical for these seasons. In the spruce forest the N 2 O uptake was seasonally decoupled from the CH 4 uptake. Conclusions Applying the Global Warming Potential (GWP) approach, the cooling effect of N 2 O uptake in the spruce forest was on average 35% of that of CH 4 uptake showing that N 2 O uptake should be considered when evaluating the atmospheric impact of boreal forests.