Methane production potential and methanogenic archaeal community structure in tropical irrigated Indian paddy soils

Soil characteristics regulate various belowground microbial processes including methanogenesis and, consequently, affect the structure and function of methanogenic archaeal communities due to change in soil type which in turn influences the CH₄production potential of soils. Thus, five different soil orders (Alfisol, Entisol, Inceptisol, Podzol and Vertisol) were studied to assess their CH₄production potential and also the methanogenic archaeal community structure in dryland irrigated Indian paddy soils. Soil incubation experiments revealed CH₄production to range from 178.4 to 431.2 μg CH₄g⁻¹dws in all soil orders as: Vertisol<Inceptisol<Entisol<Podzol<Alfisol. The numbers of methanogens as quantified using real-time quantitative polymerase chain reaction (qPCR) targeting mcrA genes varied between 0.06 and 72.97 (×10⁶copies g⁻¹dws) and were the highest in Vertisol soil and the least in Alfisol soil. PCR-denaturing gradient gel electrophoresis (DGGE)-based approach targeting 16S rRNA genes revealed diverse methanogenic archaeal communities across all soils. A total of 43 DGGE bands sequenced showed the closely related groups to Methanomicrobiaceae, Methanobacteriaceae, Methanocellales, Methanosarcinaceae, Methanosaetaceae and Crenarchaeota. The composition of methanogenic groups differed among all soils and only the Methanocellales group was common and dominant in all types of soils. The highest diversity of methanogens was found in Inceptisol and Vertisol soils. Methane production potential varied significantly in different soil orders with a positive relationship (p < 0.05) with methanogens population size, permanganate oxidizable C (POXC) and CO₂production. The present study suggested that CH₄production potential of different soils depends on physicochemical properties, methanogenic archaeal community composition and the population size.