Liming mitigates earthworm-induced CO2 and N2O emissions from a sugar maple (Acer saccharum Marsh.) forest soil

Abstract

Sugar maple (Acer saccharum Marsh.) forests in southern Quebec (Canada) are used for multiple human activities, with potential impacts on soil greenhouse gas emissions. Here, we studied the principal and interactive effects of three anthropogenic factors, namely (1) changes in leaf litter quality due to stand conversion, (2) application of dolomitic lime, and (3) the introduction of non-native earthworms, on soil CO₂ and N₂O emissions and related soil properties. These three experimental factors were arranged in a 2 × 2 × 2 factorial array to obtain eight treatments that we replicated four times in a complete randomized block design. Treatments were applied to mesocosms containing sugar maple forest soil and incubated for 15 months, during which we monitored soil CO₂ and N₂O emissions. At the end of the trial, we sampled soils at four depths and measured pH, mineralizable nitrogen, soil aggregate stability (WSAI), δ¹³C, and mineral-associated organic matter (MAOM). Liming reduced CO₂ emissions across all earthworm × litter-type combinations. By contrast, earthworms increased CO₂ only when combined with the sugar maple-American beech (Fagus grandifolia Ehrh.) litter mixture. Both liming and earthworms increased WSAI. However, we found a negative relationship between WSAI and cumulative CO₂ in soils (0–20 cm depth) without earthworms, but a positive relationship between these two variables in soils without liming. These two contrasting relationships highlight the biochemical differences in aggregates formed by liming and those formed by earthworms. Earthworms increased both nitrification and N₂O emissions whereas liming increased soil pH while reducing the positive effect of earthworms on N₂O. We found no treatment effects of either δ¹³C or MAOM. We conclude that the spread of non-native earthworms in sugar maple forests of southern Quebec will potentially increase soil N₂O and CO₂ emissions, but these could be mitigated by liming.