Effects of liming on oxic and anoxic N₂O and CO₂ production in different horizons of boreal acid sulfate soil and non-acid soil under controlled conditions

In acid sulfate (AS) soils, organic rich topsoil and subsoil horizons with highly variable acidity and moisture conditions and interconnected reactions of sulfur and nitrogen make them potential sources of greenhouse gases (GHGs). Subsoil liming can reduce the acidification of sulfidic subsoils in the field. However, the mitigation of GHG production in AS subsoils by liming, and the mechanisms involved, are still poorly known. We limed samples from different horizons of AS and non-AS soils to study the effects of liming on the N₂O and CO₂ production during a 56-day oxic and subsequent 72-h anoxic incubation. Liming to pH ≥ 7 decreased oxic N₂O production by 97–98 % in the Ap1 horizon, 38–50 % in the Bg1 horizon, and 34–36 % in the BC horizon, but increased it by 136–208 % in the C horizon, respectively. Liming decreased anoxic N₂O production by 86–94 % and 78–91 % in Ap1 and Bg1 horizons, but increased it by 100–500 % and 50–162 % in BC and C horizons, respectively. Liming decreased N₂O/(N₂O + N₂) in anoxic denitrification in most horizons of both AS and non-AS soils. Liming significantly increased the cumulative oxic and anoxic CO₂ production in AS soil, but less so in non-AS soil due to the initial high soil pH. Higher carbon and nitrogen contents in AS soil compared to non-AS soil agreed with the respectively higher cumulative oxic N₂O production in all horizons, and the higher CO₂ production in the subsoil horizons of all lime treatments. Overall, liming reduced the proportion of N₂O in the GHGs produced in most soil horizons under oxic and anoxic conditions but reduced the total GHG production (as CO₂ equivalents) only in the Ap1 horizon of both soils. The results suggest that liming of subsoils may not always effectively mitigate GHG emissions due to concurrently increased CO₂ production and denitrification.