Responses of Methanogenic and Methanotrophic Communities to Elevated Atmospheric CO(2) and Temperature in a Paddy Field

Although climate change is predicted to affect methane (CH(4)) emissions in paddy soil, the dynamics of methanogens and methanotrophs in paddy fields under climate change have not yet been fully investigated. To address this issue, a multifactor climate change experiment was conducted in a Chinese paddy field using the following experimental treatments: (1) enrichment of atmospheric CO(2) concentrations (500 ppm, CE), (2) canopy air warming (2°C above the ambient, WA), (3) combined CO(2) enrichment and warming (CW), and (4) ambient conditions (CK). We analyzed the abundance of methanogens and methanotrophs, community structures, CH(4) production and oxidation potentials, in situ CH(4) emissions using real-time PCR, T-RFLP, and clone library techniques, as well as biochemical assays. Compared to the control under CE and CW treatments, CH(4) production potential, methanogenic gene abundance and soil microbial biomass carbon significantly increased; the methanogenic community, however, remained stable. The canopy air warming treatment only had an effect on CH(4) oxidation potential at the ripening stage. Phylogenic analysis indicated that methanogens in the rhizosphere were dominated by Methanosarcina, Methanocellales, Methanobacteriales, and Methanomicrobiales, while methanotrophic sequences were classified as Methylococcus, Methylocaldum, Methylomonas, Methylosarcina (Type I) and Methylocystis (Type II). However, the relative abundance of Methylococcus (Type I) decreased under CE and CW treatments and the relative abundance of Methylocystis (Type II) increased. The in situ CH(4) fluxes indicated similar seasonal patterns between treatments; both CE and CW increased CH(4) emissions. In conclusion results suggest that methanogens and methanotrophs respond differently to elevated atmospheric CO(2) concentrations and warming, thus adding insights into the effects of simulated global climate change on CH(4) emissions in paddy fields.