Enriched anoxic methanotrophic consortium augmentation for mitigating methane emissions in rainfed systems and climate-neutral rice production

Abstract

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 (Vmax 45.70 ± 13.71 μmol-CH4⋅g−1⋅h−1 and Km 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.