Water-saving irrigation practices in rice paddies reverse the impact of root aerenchyma on methane emissions

Rice root aerenchyma (RA) and irrigation practices influence key physiological processes in rice paddies, affecting both yield and methane (CH4) emissions. However, the interaction between RA and irrigation practices, and its implications for CH4 mitigation, remains unclear, making it difficult to identify rice cultivars for CH4 mitigation purposes. Here, we conducted a series of field and pot experiments to evaluate how RA affects grain yield and CH4 emissions under two common irrigation regimes: continuous flooding (CF) and alternate wetting and drying (AWD). Our results show that the interaction between RA and irrigation regime significantly influenced both rice yield and CH4 emissions. Under CF, increased RA formation was associated with higher rice yield and lower CH4 emissions across a wide range of cultivars. These results could be explained by cultivars with well-developed RA increasing root oxygen loss, thereby stimulating CH4 oxidation and promoting N availability to support plant growth. In AWD systems, no significant differences in rice yield, methanogenesis or methanotrophy were observed between cultivars with varying RA development. However, cultivars with well-developed RA increased CH4 emissions by 28 %−32 % compared to those with less-developed RA, likely due to enhanced CH4 transport from anaerobic deep soil layers to the atmosphere. Consistent with these findings, CH4 emissions under AWD decreased when we inhibited RA development through root irrigation with brassinosteroids. In conclusion, we demonstrate that AWD in paddies can reverse the impact of RA on CH4 emissions, highlighting the need for CH4 mitigation strategies involving cultivar selection to account for variations in irrigation practices. [Display omitted] •AWD could significantly reduce CH4 emissions compared with CF.•Developed RA stimulates CH4 oxidation and reduces emissions in CF.•AWD produces more CH4 in deep soil than in surface soil.•Developed RA promotes CH4 transport and increases CH4 emission under AWD.•Optimal cultivars for CH4 mitigation strongly depend on water management practices.