Response of nitrite-dependent anaerobic methanotrophs to elevated atmospheric CO concentration in paddy fields.

Nitrite-dependent anaerobic methane oxidation (n-damo) catalyzed by Candidatus Methylomirabilis oxyfera (M. oxyfera)-like bacteria is a new pathway for the regulation of methane emissions from paddy fields. Elevated atmospheric CO concentrations (e[CO]) can indirectly affect the structure and function of microbial communities. However, the response of M. oxyfera-like bacteria to e[CO] is currently unknown. Here, we investigated the effect of e[CO] (ambient CO + 200 ppm) on community composition, abundance, and activity of M. oxyfera-like bacteria at different depths (0-5, 5-10, and 10-20 cm) in paddy fields across multiple rice growth stages (tillering, jointing, and flowering). High-throughput sequencing showed that e[CO] had no significant effect on the community composition of M. oxyfera-like bacteria. However, quantitative PCR suggested that the 16S rRNA gene abundance of M. oxyfera-like bacteria increased significantly in soil under e[CO], particularly at the tillering stage. Furthermore, CH tracer experiments showed potential n-damo activity of 0.31-8.91 nmol CO g (dry soil) d. E[CO] significantly stimulated n-damo activity, especially at the jointing and flowering stages. The n-damo activity and abundance of M. oxyfera-like bacteria increased by an average of 90.9% and 50.0%, respectively, under e[CO]. Correlation analysis showed that the increase in soil dissolved organic carbon content caused by e[CO] had significant effects on the activity and abundance of M. oxyfera-like bacteria. Overall, this study provides the first evidence for a positive response of M. oxyfera-like bacteria to e[CO], which may help reduce methane emissions from paddy fields under future climate change conditions.