Combined Effects of Elevated Ozone and Warming on Methanogenesis in Paddy Soil Across Depths

Elevated tropospheric ozone (O 3 ) concentrations and global warming represent critical environmental challenges; however, their combined impacts, particularly the indirect influences on methanogenesis in paddy soils, remain poorly understood. To clarify how methanogenesis responds to elevated O 3 (1.5 × ambient) and warming (+ 2 °C), we sampled surface (0–10 cm) and subsurface (10–20 cm) soils throughout two rice seasons in an O 3 -T-FACE (Free-Air Controlled Environment) platform and measured CH 4 production potential via anoxic incubation. The results showed that elevated O 3 levels increased the CH 4 production potential in surface soil by 22–836% compared to the control, whereas warming effects varied with the growth stage. Notably, their combined effects amplified CH 4 production potential in surface soils by 32–1214%, possibly owing to increases in initial dissolved organic carbon (DOC, 19–38%), microbial biomass carbon (MBC, 10–32%), methanogen abundance (28–97%), and DOC consumption during incubation (29–131%). In subsurface soils, elevated O 3 levels and warming individually enhanced CH 4 production potential by 5–38% and 4–101%, respectively, with their combined effect increasing it by 29–101%, linked to elevated methanogen abundance (4–290%) and DOC consumption (4–56%). Random forest and Partial Least Squares Path Modeling (PLS-PM) analyses collectively identified soil DOC concentration, DOC consumption, and CH 4 cycle-related microbial abundance as key determinants of methanogenesis across soil depths. These results underscore the dual control of abiotic and biotic factors on methanogenesis under future O 3 and warming, revealing a “surface sensitivity-subsurface buffering” pattern in paddy-ecosystem responses to elevated O 3 and warming.