Atmospheric impact of nitrous oxide uptake by boreal forest soils can be comparable to that of methane uptake

Abstract

Aims Environmental factors controlling nitrous oxide (N2O) uptake in forest soils are poorly known, and the atmospheric impact of the forest N2O sink is not well constrained compared to that of methane (CH4). Methods We compared nitrous oxide (N2O) and CH4 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 N2O and CH4 fluxes. Results Non-fertilized spruce forest soils showed the highest cumulative N2O uptake among the sites, whereas the pine forest site displayed low cumulative N2O emission. Nitrous oxide uptake was favored by high soil silt and water content. The low temperature seasons, spring and autumn, had the highest N2O uptake, likely associated with high soil water content typical for these seasons. In the spruce forest the N2O uptake was seasonally decoupled from the CH4 uptake. Conclusions Applying the Global Warming Potential (GWP) approach, the cooling effect of N2O uptake in the spruce forest was on average 35% of that of CH4 uptake showing that N2O uptake should be considered when evaluating the atmospheric impact of boreal forests.

Nitrous Oxide Fluxes in Permafrost Peatlands Remain Negligible After Wildfire and Thermokarst Disturbance

“…The Peat Plateaus in this study had the lowest P supply and PO 4 3− porewater concentrations compared to the other stages, which could have limited N 2 O emissions (Liimatainen et al., 2018). Besides N 2 O uptake, we also observed CH 4 uptake by the peat plateaus due to the oxic soil conditions, similar to other studies on boreal forests (Siljanen et al., 2020) and tundra peat plateaus (Voigt, Lamprecht, et al., 2017). As in Gibson et al.…”

How does management affect soil C sequestration and greenhouse gas fluxes in boreal and temperate forests? – A review

“…The release or sink of N 2 O is mainly associated with the nitrification and denitrification process, where soil microorganisms such as nitrifiers and denitrifiers play an important role in the biological transformation of N. The effects of N fertilization on soil N 2 O emission or uptake are highly dependent on the soil environment. For example, the uptake of N 2 O was favored by high soil silt and water content (Siljanen et al, 2020). The N induced increase in N 2 O emission through nitrification or denitrification appears to be soil pH dependent with increases in emissions not always observed in acid boreal forest soils (Saarsalmi and Mälkönen, 2001;Smolander et al, 1995).…”

“…Although methane (CH 4 ) and nitrous oxide (N 2 O) fluxes are much lower than the amount of CO 2 uptake in forest ecosystems, the global warming potentials (GWP) of CH 4 and N 2 O are almost 30 and 300 times higher than that of CO 2 , respectively. Siljanen et al (2020) emphasized the importance of evaluating soil N 2 O fluxes because the cooling effect of N 2 O uptake was on average 35% of that of CH 4 uptake in a spruce forest.…”

“…Overall, the effects of fertilization on GHG emission or uptake appears to be dependent on soil water content, soil silt content, soil pH, fertilization addition rate, and the time since fertilization (Brumme and Beese, 1992;Håkansson et al, 2021;Jassal et al, 2011;Siljanen et al, 2020;Sitaula et al, 1995;Xia et al, 2020).…”

“…Interpretation of changes in total soil respiration is challenging whenever major changes in vegetation composition occur as well, since those may affect root production and the proportion of autotrophic root respiration. Overall, the effects of WA fertilization on GHG emission or uptake appears to be dependent on soil water content, soil silt content, soil pH, fertilization addition rate, and the time since fertilization (Brumme and Beese, 1992;Håkansson et al, 2021;Jassal et al, 2011;Siljanen et al, 2020;Sitaula et al, 1995;Xia et al, 2020).…”