Growing season nitrous oxide fluxes across a 125+ year harvested red spruce forest chronosequence

Forest harvesting alters the cycling of nitrogen (N) within temperate forest systems in a manner that may influence atmospheric nitrous oxide (N₂O) concentrations. This paper investigates, over a single growing season within the Acadian Forest region of Atlantic Canada, soil N₂O fluxes across a clearcut harvest red spruce forest chronosequence that includes an old growth reference site (>125 years). A pulse of soil N₂O at ~1–2 years was observed after clearcut harvesting, followed by an exponential decay to a baseline level within one to two decades after the harvesting event. No significant differences between fluxes from the forest sites >20 years of age and the reference old growth site (>125 years) were observed. Soils within the chronosequence acted as both sources and sinks for N₂O through the growing season. Low soil N availability was identified as the likely factor limiting soil N₂O flux responses to changes in soil temperature and moisture in situ at most sites. This was confirmed by controlled laboratory experiments that measured soil N₂O flux responses to moisture, temperature and N amendments. Without N amendments, soils act as an elevated sink for N₂O under increased temperature. However, when soil N was not limiting, N₂O flux responded primarily to moisture. Overall, the study suggests that moist temperate forest soils that are N-limited can act as a transient source of N₂O following clearcut harvesting during the growing season, and that the decrease in the release of N₂O from soils following harvesting follows an exponential pattern.