Earthworms regulate the response of greenhouse gas emissions in wetland soils to simulated warming and flooding

Wetlands are a significant source of greenhouse gases (GHGs) and provide crucial habitats for soil invertebrates. Climate change, including warming and increased flooding, has considerably altered the exchange of GHGs between wetland soils and the atmosphere. However, whether and how soil fauna regulates the impacts of climate change on GHGs remains obscure. Herein, we conducted a 58-day microcosm incubation of wetland soils at two temperatures (20 and 25 °C) and two soil moisture levels (90 % and 135 % water-filled pore space) to investigate how earthworms (Eisenia fetida) regulate the direction and magnitude of GHG (CO₂, CH₄, and N₂O) responses to simulated warming and flooding scenarios. Results showed that warming increased emissions of all three GHGs, whereas flooding increased CH₄ emissions but suppressed CO₂ and N₂O emissions. Earthworms changed these response patterns by interacting with temperature and soil moisture conditions. Earthworms mitigated the positive effects of warming on CO₂ and N₂O but strengthened the positive influences of warming on CH₄, and they converted the negative response of CO₂ to flooding to positive but did not change the response of CH₄ and N₂O to flooding. In addition, Hierarchical partitioning analysis revealed that soil nitrogen availability (including NH₄⁺-N, NO₃⁻-N, and water-soluble nitrogen) and soil aggregates are the dominant factors driving the response of GHG emissions to earthworm activities and climate change. Overall, our findings highlight the crucial role of soil fauna in regulating GHG responses to warming and flooding in wetland soils, with significant implications for climate change mitigation.