Nitrous oxide emissions from soil during freezing and thawing periods

Abstract

In a laboratory investigation, the processes of N 2O emissions during freezing/thawing periods were studied. Four undisturbed soil columns from an agricultural site were subjected to two freeze/thaw cycles. Two periods of higher N 2O emissions were detected, a period of elevated N 2O emissions during continuous soil freezing and a period of brief peak emissions during thawing. Soil respiration indicated that microorganisms were still active in both periods. We concluded that N 2O was produced by microorganisms during continuous soil freezing in an unfrozen water film on the soil matrix. This thin liquid water film was covered by a layer of frozen water. The frozen water in form of an ice layer represents a diffusion barrier which reduces oxygen supply to the microorganisms and partly prevents the release of the N 2O. Peak emissions during soil thawing were explained by the physical release of trapped N 2O and/or denitrification during thawing.