Earthworm invasion and interaction with litter increased CO2 and N2O emissions in Changbai Mountain: A microcosm study

Climate change is changing the elevational pattern of soil fauna in the mountain system, leading to their upward invasion process. Earthworm invasion activity contributes to greenhouse gas emissions and soil nutrients. However, the effect of earthworm invasion on gas emission, and the contributions of interaction with litter have not been clearly understood. In this study, we conducted a microcosm study of soil samples collected from four vegetation zones in Changbai Mountain to determine the effect of earthworms, litter, and their interactions on soil CO₂ and N₂O emissions. Soil samples were incubated in the laboratory at the average soil temperature in each vegetation zone during summer for 71 days. Our findings indicate that the CO₂ gas emission rate (RCO₂) first increased and then decreased, whereas the N₂O gas emission rate (RN₂O) decreased with increasing elevation. During the microcosm study, the addition of litter decelerated the rate of decline in earthworm biomass. Earthworm-, litter-, and the interactions-induced RCO₂ increased by 19.7–44.2 %, 72.8–96.3 %, and 104.1–131.6 %, respectively. Litter-induced (SL and SLE) RN₂O was higher (1.24–10 and 5.5–16 times) compared to S except in coniferous and broad-leaved forests, with SLE showing the highest values (0.11–1.23 μg kg⁻¹ h⁻¹). The impacts of earthworms and litter on greenhouse gases were not a simple additive effect. Environmental factors explained 35.34 % and 42.83 % of the total variations in RCO₂ and RN₂O emissions, respectively, in which NO₃⁻-N contributed the largest variations. Piecewise structural equation modeling (SEM) results underscored the interplay between elevation, earthworms, litter, and soil properties in affecting soil CO₂ and N₂O emissions. Earthworms, litter, and their interactions could affect CO₂ and N₂O emissions, and these variations were predominantly controlled by environmental factors. Our study provides valuable insights into how litter input and earthworm invasion influence soil carbon and nitrogen cycling. With the background of global climate change, the synergistic response of soil fauna invasion and greenhouse gas emissions to warming be an integral part of future risk assessment, and that to evaluate soil process, both the soil fauna and environmental factors must be taken into account.