Enriched anoxic methanotrophic consortium augmentation for mitigating methane emissions in rainfed systems and...

This study demonstrated the effectiveness of enriched anoxic methanotrophic consortium augmentation in reducing methane (CH₄) emissions from rice cultivation while improving soil fertility and rice productivity. The enriched consortium from cattle farm effluent, dominated by Acinetobacter (65.5%) and containing both types I (Methylosarcina, Methylomagnum, and Methyloversatilis) and II (Methylocystis) methanotrophs, exhibited high methane oxidation rates (V_max 45.70 ± 13.71 μmol-CH₄⋅g^-1⋅h^-1 and K_m 16.50 ± 4.95 μM). The optimal inoculum size for soil application was 0.2 L⋅m^-2 (OD₆₀₀ = 0.5), resulting in a CH₄ reduction efficiency of 74.30 ± 3.56%. In rice pot experiments, the anoxic methanotrophic consortium with an inoculum size of 0.2 L⋅m^-2 reduced methane emissions by 79.32 ± 3.96% without fertilizer and 29.22 ± 1.45% and 46.81 ± 1.87% when combined with organic and chemical fertilizers, respectively. The field-scale evaluation revealed that combined soil and irrigation water application with anoxic methanotrophic consortium augmentation was the most effective, reducing seasonal methane emissions from 32.8 ± 4.2 to 9.3 ± 1.5 g-CH₄·m^-2 and methane flux from 15.2 ± 2.1 to 4.3 ± 0.8 mg-CH₄·m^-2·h^-1, representing a 71.7 ± 0.4% reduction. This method also increased plant height (6.5%) and tiller number (26.4%). The combined application method also resulted in the highest soil nutrient levels (96.1 mg-N·kg^-1 soil, 21.8 mg-P·kg^-1 soil, and 133.4 mg-K·kg^-1 soil) and increased rice yield by 14.7% (975 g⋅m^-2). These findings demonstrate that anoxic methanotrophic consortium augmentation is a sustainable approach to mitigate methane emissions and improve rice productivity, emphasizing the importance of integrating this strategy into rice cultivation practices in rainfed lowland areas.