Aerobic methane oxidation in typical grassland soil

Abstract:

[Objective] The soil methane uptake potential, abundance and community structure of methane-oxidizing bacteria were investigated in three grasslands located in three different ecoregions:Maqu, Linze and Huanxian of Gansu province of China. [Methods] Eight days incubation of soil with elevated concentration of methane was carried out to measure methane uptake capacity. The methane-oxidizing bacteria abundance was quantified by real time quantitive PCR targeting particulate methane monooxygenase coding gene (pmoA) in soils. The methane-oxidizing bacteria community structure was assessed by amplicon MiSeq sequencing. [Results] The potential of methane oxidation of three grassland soils ranged from 108.53±13.12 to 168.87±18.57 mg/(m²·h). The abundance of methane-oxidizing bacteria ranged from 1.76×10⁷ to 6.86×10⁷ pmoA gene copies g/d.w.s. The methane oxidation potential was positively correlated with methane-oxidizing bacteria abundance at day 0 (R²=0.5537). MiSeq sequencing analysis revealed significant spatial heterogeneity of methane-oxidizing bacteria community within the same grassland type. The Upland Soil Cluster gamma belonging to uncultured atmospheric methane oxidizers was the dominant methanotrophic lineage within methane-oxidizing bacteria gene types found in situ grassland soils. However, the conventional methane-oxidizing bacteria increased significantly after incubated these soils under high concentration methane, such as Methylocystis in Maqu soil and Methylosarcina in Linze and Huanxian soils. [Conclusion] Both uncultured atmospheric methane-oxidizing bacteria and the conventional methane-oxidizing bacteria may play an important role in the process of methane oxidation in the typical grassland soils in Gansu province of China. These microbes are very likely to oxidize the trace methane in atmosphere, and may also grow with high concentration of methane that stored in the soil. In the future, advanced techniques should be used to observe the atmospheric methane oxidation process in situ and to isolate the corresponding microbial groups, and finally reveal the geographical differentiation of methane-oxidizing bacteria in grassland soils and the environmental driving mechanism.

Key words:grassland;methane oxidation;pmoA gene