No abstract

Microbial methane (CH4) production and emission are various in different paddy fields. However, little is known about values of anaerobically produced δ13CH4, methanogenic pathways, and their dominant communities in different paddy soils. Through anaerobic incubation experiments and the stable carbon isotope with fluoromethane inhibitor method, CH4 production potential (MPP), the relative contribution of acetoclastic methanogenesis (fac), and the abundance and community composition of methanogens in paddy soils were measured under three typical cropping modes (Rice-Wheat, RW; Rice-Fallow, RF; Double-Rice, DR) in China. The results showed that MPP was 13.4 μg CH4 g–1 d–1 in DR soil, 23% and 46% higher than that in RW and RF soils, respectively. Moreover, RF soil had the highest produced δ13CH4 value (–43.9‰) and the lowest produced δ13CO2 value (–26.3‰). Based on the isotope fractionations associated with H2/CO2-dependent methanogenesis (1.049–1.062), fac values in RF soil (80–98%) were much higher than that in RW (39–60%) and DR (52–75%) soils. Compared to RF soil, mcrA gene abundance in RW and DR soils increased by 29% and 40%, respectively. Furthermore, the dominant methanogens in RF soil were Methanosarcina (acetoclastic methanogens) while Methanosarcina and Methanobacterium (hydrogenotrophic methanogens) were in RW and DR soils. Redundancy analysis revealed that soil pH and soil texture affected the community structure of methanogens. These findings suggest that differences in paddy MPP and methanogenic pathways under the three typical cropping modes might be caused by the changes in methanogenic abundance and community composition driven by soil pH.