Effect of elevated atmospheric CO2 concentration on the activity, abundance and community composition of aerobic methanotrophs in paddy soils

The elevated atmospheric CO2 concentration (eCO(2)) has a great impact on soil microbial communities and their functions; however, how the activity and communities of methanotrophs respond to eCO(2) in paddy ecosystem is poorly known. Here, we examined the effects of a 4-year exposure to eCO(2) (EC; ambient + 200 ppm) in open top chambers on the potential activity, abundance and community composition of methanotrophs in paddy fields in Nanjing City, China. The potential activity was measured in a slurry incubation under aerobic condition, and the community composition and abundance of methanotrophs were analyzed through Illumina Miseq sequencing and quantitative PCR of pmoA genes. The results demonstrated that EC significantly increased (p < 0.05) the methane oxidation potential and pmoA gene abundance of methanotrophs by 52.9%-56.7% and 83.5%-213.6%, respectively, during late rice growth stages as compared with ambient condition (CK). Further, the community composition of methanotrophs in soil changed significantly (p < 0.05), with the dominant methanotrophs shifting from type II under CK to type I under EC. The variation of soil dissolved organic carbon and inorganic nitrogen levels caused by eCO(2) had an important impact on the methane oxidation potential and methanotrophic community structure. Taken together, our results indicate that eCO(2) can have an important impact on the activity, abundance and community composition of methanotrophs, adding new insights into the effects of rising CO2 on methane cycling in paddy ecosystems.