Methanotrophs Contribute to Nitrogen Fixation in Emergent Macrophytes.

Root-associated aerobic methanotroph plays an important role in reducing methane emissions from wetlands. In this study, we examined the activity of methane-dependent nitrogen fixation and active nitrogen-fixing bacterial communities on the roots of and using a N-N feeding experiment and a cDNA-based clone library sequence of the gene, respectively. A N-N feeding experiment showed that the N fixation rate of (1.74 μmol h g dry weight) was significantly higther than that of (0.48 μmol h g dry weight). The presence of CH significantly increased the incorporation of N-labeled N into the roots of both plants, and the rate of CH-dependent N fixation of (5.6 μmol h g dry weight) was fivefold higher than that of (0.94 μmol h g dry weight). The active root-associated diazotrophic communities differed between the plant species. Diazotrophic of the was dominant in , while of the was dominant in . However, there were no significant differences in the copy numbers of between plant species. These results suggest that N fixation was enhanced by the oxidation of CH in the roots of macrophytes grown in natural wetlands and that root-associated , including , contribute to CH oxidation-dependent N fixation.