EGU26-16855, updated on 14 Mar 2026
https://doi.org/10.5194/egusphere-egu26-16855
EGU General Assembly 2026
© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.
Oral | Monday, 04 May, 15:15–15:25 (CEST)
 
Room 1.31/32
Cover crops, soil depth and nutrient dynamics drive N2O emissions and N2O forming processes during soil freezing and thawing
Mari Pihlatie1,2, Osmo Virta1,2, Heidi Aaltonen1,2, Jonna Teikari1,2,3, Pauliina Turunen1,2, Lukas Kohl4, Matej Znamínko4,5, Carlos Palacin Lizarbe4, Hannu Nykänen4, Christina Biasi5, and Markku Koskinen1,2
Mari Pihlatie et al.
  • 1University of Helsinki, Faculty of Agriculture and Forestry, Department of Agricultural Sciences, Helsinki, Finland (mari.pihlatie@helsinki.fi)
  • 2Institute for Atmospheric and Earth System Research (INAR)/Faculty of Agriculture and Forestry, University of Helsinki, Helsinki, Finland
  • 3University of Helsinki, Faculty of Agriculture and Forestry, Department of Microbiology, Helsinki, Finland
  • 4University of Eastern Finland, Department of Environmental and Biological Sciences, Kuopio, Finland
  • 5University of Innsbruck, Department of Ecology, Innsbruck, Austria

Freeze–thaw cycles (FTCs) are recognized as important regulators of nitrous oxide (N₂O) emissions in temperate and boreal soils, yet the underlying drivers and processes during FTC remain poorly understood. 

We set up two controlled incubation experiments to investigate the effect of freezing and thawing on N2O emissions, emission drivers and N2O forming processes. Soil samples were collected during spring freeze-thaw period from a biodiversity cover crop plot trial in Helsinki, southern Finland. In experiment 1, we studied the effects of soil depth and cover crops (CC) on N₂O emissions, soluble nutrients (N, P, C) and active N cycling genes (RNA) during consecutive freezing and thawing phases over a 3-week period. In experiment 2, we studied N2O emissions and their isotopologue ratios in a dynamic automated FTC experiment with alternating freezing (–4 °C) and thawing (+4 °C) cycles. To support the controlled experiments, we conducted twice weekly N2O flux measurements in the field during the spring freezing-thawing period.

Throughout the experiment 1, we found significantly greater N2O production at the surface (0 – 2 cm) compared to the subsurface (9 – 11 cm) soil depth. To support this, soil nitrate, ammonium, total dissolved N, dissolved organic C and soluble reactive P concentrations where higher in the topsoil compared to the subsurface. In experiment 2, N2O emissions occurred during thawing periods but were stimulated by freezing. Based on isotopologue ratios, the N2O originated predominantly from denitrification. Field N2O flux data support the laboratory results showing higher N2O emissions during freeze-thaw, and smaller during warm periods, and that cover crop treatments potentially lead to higher N2O emissions during soil freeze-thaw. Overall, the findings demonstrate the episodic nature of freeze-thaw related N2O emissions governed by substrate dynamics in soil that support conditions suitable for “hot moments”.

How to cite: Pihlatie, M., Virta, O., Aaltonen, H., Teikari, J., Turunen, P., Kohl, L., Znamínko, M., Palacin Lizarbe, C., Nykänen, H., Biasi, C., and Koskinen, M.: Cover crops, soil depth and nutrient dynamics drive N2O emissions and N2O forming processes during soil freezing and thawing, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16855, https://doi.org/10.5194/egusphere-egu26-16855, 2026.