IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 BOOK OF ABSTRACTS 206 Poster Session / Soil Organic Matter, Caustobiolites, and Biochar Hall A P2.11 Redox-Driven Coupling of Natural Organic Matter Dynamics and Greenhouse Gas Fluxes in Subtropical Paddy Rice Chuan-Fu Kao1, Shan-Li Wang1 1 Department of Agricultural Chemistry, National Taiwan University, Taipei 106319, Taiwan Email: wangsl@ntu.edu.tw Subtropical paddy fields are critical interfaces in the global carbon (C) cycle, functioning as major anthropogenic methane (CH4) sources while offering potential for soil organic carbon (SOC) sequestration. Under double-cropping systems, high temperatures and intense precipitation generate dynamic redox gradients that govern tradeoffs between greenhouse gas (GHG) mitigation and C stabilization. This study investigates how hydrological redox regimes and rice straw (RS)-derived organic carbon (OC) regulate C–N coupling and SOC dynamics. Using a high-frequency automated chamber system, we quantified CH4 and N2O fluxes alongside SOC changes across six management scenarios: conventional flooding (CF) and alternate wetting and drying (AWD), each combined with RS removal, incorporation, or surface cover. CH4 dominated global warming potential (GWP), contributing 90–98% under continuously anaerobic conditions. Although OC inputs via RS supplied labile substrates that initially stimulated methanogenesis, AWD reduced seasonal GWP by 24.3–79.5% through periodic oxidative shifts. The effectiveness of these strategies was strongly climate-dependent. Earlier CH4 emission peaks in the second cropping season reflected accelerated residue decomposition under warmer conditions, indicating a thermal–substrate legacy effect on methanogenesis. Notably, a biogeochemical trade-off emerged: AWD combined with RS surface cover produced the highest episodic N2O emissions, likely driven by rapid C–N coupling during transient redox oscillations. In terms of carbon balance, continuous RS removal led to SOC losses of up to 1.6 t C ha⁻¹ yr⁻¹, whereas RS incorporation achieved net sequestration rates of 1.4–1.8 t C ha⁻¹ yr⁻¹. These results demonstrate that integrating AWD with optimized RS management can reconcile GHG mitigation with SOC sequestration. By elucidating redox-driven controls on OC/SOC dynamics, this work provides a mechanistic basis for developing carbonneutral and soil-stabilizing strategies in subtropical agroecosystems. Keywords: Rice straw management; Soil organic carbon; Greenhouse gas mitigation; Alternate wetting and drying; Redox-driven processes; Carbonnitrogen coupling
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