Effects of Extreme Moisture Events on Greenhouse Gas Emissions and Soil Ecological Functional Stability in Calcaric Cambisols

Global warming is expected to increase the frequency and intensity of extreme precipitation, yet its effects on soil greenhouse gas (GHG) emissions and functional stability remain uncertain. This study explored the impact of extreme soil moisture conditions on farmland and forest soil under three scenarios: 60% field water capacity (W1), soil saturation (W2), and 10 cm of standing water (W3). We used a laboratory incubation to evaluate how three extreme soil moisture regimes—60% of field water capacity (W1), soil saturation (W2), and 10 cm of standing water (W3)—affect GHG emissions and the functional stability of farmland and forest soils. Forest soils exhibited significantly higher global warming potential (GWP) than farmland across all regimes (p < 0.05). Relative to W1, farmland GWP increased by 0.14% under W3, whereas forest GWP increased by 13.7% under W2 (p < 0.05). Extreme soil moisture conditions markedly elevated total organic C (TOC) and ammonium N (NH4+–N) contents in soil solutions from both farmland and forest, with increases of 25.0% and 6.0% for TOC and 78.6% and 69.6% for NH4+–N, respectively. Conversely, nitrate N (NO3−–N) content in farmland soil decreased by 3.54% and 6.96% under W2 and W3 treatments, while forest soil NO3−–N increased by 39.68% under W2 and decreased by 39.13% under W3. Functional stability declined under extreme precipitation and was positively correlated with total CO2 emissions, GWP, and TOC (p < 0.001), as well as with total N2O emissions and soil total C (p < 0.05). Overall, forest soils maintained greater functional stability than farmland under extreme moisture. These findings clarify how extreme soil-moisture events influence soil functional stability in a warming climate and highlight the potential for post-event recovery of soil functions.