Methanotrophs Contribute to Nitrogen Fixation in Emergent Macrophytes
Jing Cui, Meng Zhang, Linxia Chen, Shaohua Zhang, Ying Luo, Weiwei Cao, Ji Zhao, Lixin Wang, Zhongjun Jia, Zhihua Bao
Abstract
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 Typha angustifolia and Scirpus triqueter using a 15 N-N 2 feeding experiment and a cDNA-based clone library sequence of the nifH gene, respectively. A 15 N-N 2 feeding experiment showed that the N 2 fixation rate of S. triqueter (1.74 μmol h –1 g –1 dry weight) was significantly higther than that of T. angustifolia (0.48 μmol h –1 g –1 dry weight). The presence of CH 4 significantly increased the incorporation of 15 N-labeled N 2 into the roots of both plants, and the rate of CH 4 -dependent N 2 fixation of S. triqueter (5.6 μmol h –1 g –1 dry weight) was fivefold higher than that of T. angustifolia (0.94 μmol h –1 g –1 dry weight). The active root-associated diazotrophic communities differed between the plant species. Diazotrophic Methylosinus of the Methylocystaceae was dominant in S. triqueter , while Rhizobium of the Rhizobiaceae was dominant in T. angustifolia . However, there were no significant differences in the copy numbers of nifH between plant species. These results suggest that N 2 fixation was enhanced by the oxidation of CH 4 in the roots of macrophytes grown in natural wetlands and that root-associated Methylocystacea , including Methylosinus , contribute to CH 4 oxidation-dependent N 2 fixation.